The Scratch Posts

The main purpose of this blog is to help primary school teachers and student teachers develop sufficient skills and confidence to be able to use Scratch to help the children they teach learn how to write computer programs.

For more information about Scratch see - Finding your way around Scratch

The Tutorials

There is no particular order to the tutorials; they are complementary rather than sequential. They are all technically similar, though some concepts involved in the tutorials are more challenging than others. However, with programming, the acquisition of a concept is largely dependent on the motivation and needs of the learner - the more you want to learn something, the more likely you are to understand.

Tutorial	Techniques
Space Invader A shoot-em-up game based loosely on Space Invaders. The player controls a laser cannon at the base of the screen to shoot at an alien which appears randomly.	Importing a background Painting Sprites Keyboard input for moving sprites Random movement of a Sprite Duplicating Scripts Importing and playing sounds Collision detection (touching Sprites) Changing Sprite costumes in response to a collision Variables for keeping score and high score Green Flag scripts Forever loop If loop
Pong Based on the early Pong game, with only one player (ie more like a game of squash).	Drawing backgrounds Drawing sprites Importing sprites Green Flag scripts Key press scripts Sprite touching sprite collision detection Sprite touching colour detection Adding sound to sprites Updating score variable Updating High Score variable Changing sprite costumes
Shark Attack The player controls a shark moving around a fish tank to eat fish	Painting backgrounds Painting Sprites Importing a Sprite image Scripting continuous movement of Sprites Controlling Sprite movement with the keyboard Detecting and responding when Sprites touch Showing and hiding Sprites Copying Scripts between Sprites Removing blocks from Scripts Variables for Scoring Using a timer to terminate a game Using If and repeat until loops Communicating with the player through a say block
River trip Guide a boat along a river, avoiding obstacles to increase your score against a time limit Note: the concepts in this tutorial are more advanced than in the other tutorials	Painting Sprites Scrolling backgrounds Detecting when a Sprite touches a colour Forever loop If loops Using keyboard keys to move a Sprite Switching Sprite costumes after a collision Duplicating Scripts Score variable High Score variable Using a timer to terminate a game
Raindrops Catch raindrops before they hit the pavement to score points. Miss raindrops and lose points. This is a long tutorial but it does introduce a lot of concepts and programming techniques. As with Road Race, the game is playable at several points during the tutorial	Importing a background Editing a background Painting a Sprite Controlling a Sprite with the keyboard Green Flag Scripts Moving a Sprite at random speeds Positioning a Sprite randomly Collision detection between Sprites Collision detection of a Sprite and a colour Playing sounds on collision Duplicating and editing scripts Duplicating Sprites Switching Sprite costumes Switching backgrounds If loops Repeat loops Repeat Until loops Adding to and subtracting from a Score variable Setting a time limit to a game Presenting a Game Over message Updating a High Score variable Using variables for score, time countdown and High Score
Road Race The player controls a racing car steering it around the track trying to avoid running off the road and the computer controlled car.	Painting backgrounds Painting Sprites Changing Sprite costumes on collision Controlling Sprite direction with keyboard keys Green flag scripts Forever loops If loops Duplicating Scripts Duplicating Sprites and Scripts Detecting collision with touching colour? Detecting collision with touching Sprite? Using say to communicate with the player Using a variable for Lives Using a Timer to stop the game Editing Scripts
Treasure Hunt Adventure Guide Thomas around his house looking for clues as to where his brother has hidden his birthday present Note: This is the longest and most challenging tutorial, but it does introduce a lot of programming concepts and techniques	Importing backgrounds to the Stage Switching between backgrounds Using the keyboard to navigate between background scenes Adding text to a background Using broadcast and receive blocks to send messages between scripts Showing and hiding Sprites Duplicating Scripts Copying Scripts from one Sprite to another Shrinking and Growing Sprites in size Switching Sprite costumes Using say and think for speech and think bubbles Using variables to communicate a Sprite's co-ordinate position to a Script Using glide to move a sprite Ending a game with stop all
text	text

Computing National Curriculum

From September 2014, children in most primary schools in England will be required to learn how to program computers. There is no specific requirement for the children to use a particular programming environment, but by the end of their primary schooling, the National Curriculum for computing requires them to:

design, write and debug programs that accomplish specific goals, including controlling or simulating physical systems; solve problems by decomposing them into smaller parts;
use sequence, selection, and repetition in programs; work with variables and various forms of input and output;
use logical reasoning to explain how some simple algorithms work and to detect and correct errors in algorithms and programs.

On first reading, this sounds quite daunting, but with an accessible programming package such as Scratch, programming can be quite straightforward and a lot of fun!

The rationale for the tutorials

The tutorials on this blog follow a simple principle; that programming should be purposeful. The outcome of each tutorial is a game which can be played in its own right and which can be further developed into something more challenging and complex. It is possible to follow each tutorial by following the step-by-step screen-shots only, but the text is also there to help you to acquire the terminology needed to support the children's learning and also to reinforce some key concepts of programming.

Once you have acquired a set of basic skills and knowledge of techniques, it should be possible to plan and produce your own programs. With some adaptation, the tutorials could form the basis of computing lessons with KS2 children.

Each tutorial starts from 'ground zero', assuming you have little or no background knowledge of programming in Scratch. Whilst there are some basic skills inherent in every tutorial, each one includes additional unique techniques to solve a range of programming problems.

As time progresses, more tutorials will be added to extend the range of solutions to programming problems. Although some solutions are more elegant than others, with programming, an outcome can be achieved through a range of different solutions. Children (and you) should accept that there is no right or wrong way of writing a program. Either it works or it doesn't. If it works then the problem has been solved!

Introduction

I believe this game is unique, in that I've not seen one like it before. It follows a very basic principle; the player has to catch raindrops as they fall down the screen - one point gained for each raindrop caught, and one point deducted for each one missed. Seems simple, but it's harder to play than it sounds.The tutorial embodies quite a few foundation skills and techniques and, like Road Race, can be played in its own right at various stages of completion.

List of techniques

Importing a background
Editing a background
Painting a Sprite
Controlling a Sprite with the keyboard
Green Flag Scripts
Moving a Sprite at random speeds
Positioning a Sprite randomly
Collision detection between Sprites
Collision detection of a Sprite and a colour
Playing sounds on collision
Duplicating and editing scripts
Duplicating Sprites
Switching Sprite costumes
Switching backgrounds
If loops
Repeat loops
Repeat Until loops
Adding to and subtracting from a Score variable
Setting a time limit to a game
Presenting a Game Over message
Updating a High Score variable
Using variables for score, time countdown and High Score

Tutorial

	Once the program has loaded, delete the Scratch the Cat Sprite by right-clicking (Ctrl-click on a Mac) on its icon in the Sprite List Area and then clicking delete on the pop-up menu
Next, we need to create a background for the game. Click on the icon for the Stage (to the left of the Sprite List Area). Then click the Backgrounds tab above the Script Area. Now click the Edit button beside the image for background1 of the stage.
	This will take you to the Paint Editor Clear the current background image (plain white) by clicking the Clear button Now click the Import button
Double-click the Outdoors folder to open it and then click the brick-wall1 icon. Now click the OK button
	This will import the image into the Paint Editor. At this point, we do not need to edit the image and so click the OK button.
We're now ready to create a Sprite. This is an object which we can program to move around the screen. Click the Choose new sprite from file button above the Sprite List Area.
	Double click the Things folder and then click the manhole image. Now click the OK button (Note you could double-click the manhole image to select it)
The manhole is a bit too large for our game and so we need to reduce its size. Click the Shrink Sprite button above the Stage Area (on the left) and then keep clicking on the manhole sprite on the Stage Area until it is about half its original size.
	Now drag the Sprite towards the bottom of the Stage Area so it sits in the roadway by the kerb.
We are now ready to write the Scripts needed to control the manhole Sprite Click the Control button and then from the Blocks Palette, drag a when [space] key pressed block into the Script Area. Edit the block so it reads when [left arrow] key pressed
	Click the Motion button and then from the Blocks Palette, drag a point in direction [ ] block into the Script Area and then attach it to the when [left arrow] key pressed block Edit the point in direction [ ] block so it reads point in direction [-90] (left)
Now drag a move [10] steps block into the Script Area and attach it to the point in direction [-90] block You can now test your Script by pressing the left arrow key on the keyboard.
	We could repeat the above process to create a script to move the Sprite to the right, but to save time and effort we'll duplicate the Script and edit it. Right-click (Ctrl-click on a Mac) on the when [left arrow] key pressed block and on the pop-up menu click duplicate
Edit the when [left arrow] key pressed block so it reads when [right arrow] key pressed
	Now edit the point in direction block so it reads point in direction [90] (right)
Test your scripts by pressing the left and right arrow keys. You might notice that when the manhole Sprite moves to the left it flips upside down. To stop this from happening, click the only face left-right button above the Script Area.
	Now we need to create a Sprite for the manhole sprite to catch. As there are no readymade raindrop images we will have to draw our own. Click the Paint new sprite button above the Sprites List Area
This opens the Paint Editor Click a light blue colour in the Colour Palette and then the Circle tool in the toolbox. On the canvas draw a circle. It doesn't matter what size as we can resize the Sprite later.
	With the Paintbrush tool, add some more detail to make it look more like a raindrop. You can resize the Paintbrush by clicking the Brush Size button in the Options Area below the Toolbox Click OK when done
Click the Shrink Sprite button and then click on the Raindrop Sprite a few times to reduce its size.
	We're now ready to write a script for this Sprite. Click the Control button to bring up the Control Blocks in the Blocks Palette. Drag a when Green Flag clicked block into the Script Area
Now drag a Forever loop block into the Script Area and attach it to the when Green Flag clicked block.
	Drag the Sprite to the top of the Stage Area and make a note of the co-ordinates for the centre of its new location.
Click the Motion button and from the Motion Blocks Palette, drag a go to x: [ ] y: [ ] block into the Script Area and insert it into the Forever loop. You may notice that the go to block already contains the present co-ordinate location of the Sprite - also the current location is shown above the Script Area.
	From the Control Blocks Palette, drag a repeat [ ] loop block into the Forever loop beneath the go to block and edit it to read: repeat [80]
From the Motion Blocks Palette, drag a point in direction block and insert it into the repeat [80] loop. Edit the block so it reads: point in direction [180] (down)
	Insert a move [10] steps block into the repeat [80] loop and edit the block to read move [5] steps
Now test the Script by clicking the Green Flag button above the Stage Area on the right. You will notice that the Script is highlighted when it is running. To stop the Script, click the Red button beside the Green Flag button.
	You will also have noticed that the raindrop twists through 90 degrees when it falls. Sprites normally turn to face the direction they moving (as happened with the manhole Sprite). To overcome this, click the only face left-right button above the Script Area and run the Green Flag Script again.
We now need to check whether the raindrop has been caught by the manhole. From the Control Blocks Palette, insert an if loop block into the repeat [80] loop below the move [5] steps block
	From the Sensing Blocks Palette, insert a diamond-shaped touching [ ]? block into the diamond-shaped pane in the header of the If loop block. Edit the block to read If touching [Sprite1] ?
Let's make a sound when the two Sprites touch. Click the Sounds tab above the Script Area and then click the Import button
	Double-click (Ctrl-click on a Mac) the Effects folder and then click the Waterdrop file. Click the OK button to import the sound file into the Sprite.
From the Sound Blocks Palette, insert a play sound [ ] block into the If touching [Sprite1] loop If you now test the Green Flag Script you should find that the sound is made when you yo catch the raindrop with the manhole.
	We now need to detect when a raindrop has been missed. To do this we need a strip of distinctive colour towards the bottom of the Stage Area. Click the icon for the Stage beside the Sprite List Area. Then click the Backgrounds tab and then the Edit button.
Using the rectangle tool, draw a black strip across the roadway towards the base of the screen. Make sure this strip takes up about half of the roadway so there is a grey strip left below it. Click OK when done.
	Now click the Raindrop Sprite (Sprite2) icon in the Sprite List Area and then the Scripts tab to show its script in the Script Area.
From the Control Blocks Palette, insert another If loop block below the one already in the Green Flag Script, immediately below the existing If touching [Sprite1] ? loop block
	From the Sensing Block Palette, insert a touching colour [ ] ? block into the header of the If loop block
Click on the colour pane of the touching colour [ ] ? block and then click with the eye-dropper tool on the band of black that you have just created on the background of the Stage. This will transfer that colour to the pane of the touching colour [ ] ? block.
	We'll now import another sound. Click the Sounds tab and then the import button.
In the Effects folder, click the Plunge file and then the OK button.
	Click the Scripts tab and then from the Sound Blocks Palette, insert a play sound [ ] block into the if touching colour [ ]? loop. If necessary, edit the block to read play sound [Plunge] Test the Green Flag Script to compare what happens when you catch the raindrop and when you miss it.
The game is a little too easy at the moment, so let's randomise the appearance of the raindrop Sprite. From the Operators Blocks Palette, insert a pick random [ ] to [ ] block into the first pane of the go to x: [ ] y: [ ] block at the start of the forever loop in the Green Flag Script. Edit the block so it now reads: go to x: [pick random [-240] to [240] y: [166] The x co-ordinates of the Stage Area range from -240 (on the left) to 240 (on the right). The centre of the Stage Area is (0,0). Play the game by clicking the Green Flag button to see the effects of this change.
	We could do with adding some sort of scoring system. Click the Variables button and then Make a variable. Give the variable the name Score and then click OK.
Insert a set [Score] to [0] block into the Green Flag Script immediately below the when Green Flag clicked block. Insert a change [Score] by [1] block into the If [touching [Sprite1] ? ] loop (it doesn't matter if it is above or below the play sound [WaterDrop] block. Insert another change [Score] by [1] block into the If [touching colour [ ] ? ] loop and then edit the block so it reads change [Score] by [-1]. Now play the game. You'll see that the Score is now shown in the Stage Area and increases or decreases as the raindrops are caught or missed. You'll also notice that there seems to be a bug in the scoring system - this is because the raindrop Sprite touches the manhole Sprite and the black strip several times before it reaches the base of the Stage Area.
	There are several ways the bug could be overcome but I've opted to move the raindrop Sprite to the base of the screen immediately after it touches the manhole Sprite or the black strip (which is why we made the black strip only half the width of the roadway). From the Motion Blocks Palette, insert a go to x: [ ] y: [ ] block into the if [touching [Sprite1]?] loop after the two other blocks in the loop and edit the block so it reads go to x: [0] y: [-180] Insert another go to block into the other If loop and edit it in the same way. Now play the game again and, hopefully, the scoring bug will be cured. Note: If you find that the manhole Sprite touches the raindrop sprite when it has been sent to the centre of the Stage, then drag the Manhole Sprite a little higher to clear it.
Although the game is now quite playable, we can improve it still further by randomising the speed at which the raindrop Sprite descends. This will make the game more interesting when we add more raindrops. This also provides you with practice in editing an existing Script - which is useful if ever you want to change a game downloaded from the Internet. Drag the entire repeat [80] loop out of the forever loop by dragging the repeat [80] loop header downwards.
	Now drag the contents of the repeat [80] loop out of the loop by dragging the first block in the loop downwards. All the blocks attached to this first block should come with it.
Remove the repeat [80] block from the Script Area by dragging and dropping it into the Blocks Palette.
	Now drag a repeat until [ ] block into an empty space in the Script Area.
From the Operators Blocks Palette, insert a [ ] < [ ] block into the pane in the header of the repeat until block
	From the Motion Blocks Palette, insert a y position block into the first pane of the [ ] < [ ] block and then type -170 into the second pane, so the repeat until block now reads repeat until [ y position ] < [ -170 ]
Now drag the chunk of script starting with the point in direction block into the repeat until loop by dragging the first block, which should bring all the attached blocks with it.
	Now drag the repeat until block and insert it into the forever loop beneath the go to block The reason why we've changed the repeat block is that when we randomise the number of steps the raindrop Sprite takes as it descends the screen, it will require a different number of repeats to reach the bottom. By using repeat until y position < -170 the loop will keep repeating until the raindrop sprite has reached the bottom of the Stage.
We'll now create a variable to hold the value of the randomly generated step size for the raindrop's speed. Make a variable called Speed - but make sure it is for this Sprite only by clicking the radio button.
	We don't want the Speed variable to show-up on the Stage Area so uncheck the checkbox beside the Speed label.
Insert a set [ ] to [0] block into the Forever loop above the repeat until block. If necessary, edit the block so it reads set [Speed] to [0]
	Insert a pick random block into the second pane of the set [Speed] to [ ] block and edit the block to read set [Speed] to [pick random [1] to [5]]
Insert a Speed label block from the Variables Blocks Palette into the pane of the move [5] steps block in the repeat until loop so the block now reads move [Speed] steps Play the game to see the results of these changes.
	To enhance the appearance of the missed raindrop Sprites we'll now add another feature - a costume change. Click the Costumes tab and then the Paint button
Use the Paintbrush tool to create a splash image. Click OK when done.
	Click the Scripts tab to return to the Script Area
From the Looks Blocks Palette, insert a switch to costume [costume1] block into the forever loop somewhere before the repeat until loop. Insert a switch to costume [costume2] block into the if [touching colour [ ] ? ] loop somewhere before the go to x: [0] y: [-170] block
	Insert a wait [1] secs block into the if [touching colour [ ] ?] loop just above the go to x: [0] y: [-170] block
Play the game and check the effect when you miss a raindrop. If you find the splash is too small you may need to edit the costume in the Paint editor. Increasing the size of the Sprite with the Grow Sprite button will also increase the size of the raindrop.
	We'll now add another random element to the game. Insert a wait [1] secs block into the forever loop somewhere before the repeat until block
Now insert a pick random block into the wait block in place of the [1] pane and edit the blocks so they read wait [pick random [0] to [3] ] secs Play the game to check the effect of this change. Whilst this does not make an enormous difference to the game as it stands, it has a greater impact on the next change to the game.
	We're now going to duplicate the raindrop Sprite. Right-click (Ctrl-click on a Mac) the raindrop sprite icon in the Sprites List Area and then click duplicate Now try playing the game. The random speed and random timing features make the game a lot more challenging as the player needs to decide which raindrop to try and catch first. You could duplicate the raindrop again but this makes the game very difficult.
On the last leg now. To finish off the game, let's set a time limit. We'll program this as a script attached to the background. Click the Stage icon beside the Sprites List Area and create a Greeen Flag Script by dragging a when Green Flag clicked block. To this attach a forever loop block and insert into its loop an if loop block
	Into the pane of the If block header, insert a [ ] > [ ] Operator block
Insert a reset timer block just below the when Green Flag clicked block Insert a timer label block into the first pane of the [ ] > [ ] block and type 60 into the second pane so the blocks read If [[timer] > [60]]
	Insert a stop all block into the If timer > 60 loop Now play the game again. It will stop working after 60 seconds have passed. However, it would be very helpful if the player was informed that the game had finished.
Click the Backgrounds tab and then the Paint button
	You could fill the canvas with a plain colour, but let's experiment with one of the effects. Select a lighter colour for the foreground colour and a darker shade of the same colour for the background colour. Then click the graduated from centre button and then with the Fill bucket tool click on the centre of the canvas.
Use the Text tool to write Game Over using a suitable font, text size and foreground colour. Click OK when done.
	Click the Scripts tab and then insert a switch to background [background1] block just below the when Green Flag clicked block Insert a switch to background [background2] block into the if timer > 60 loop above the stop all block Check the game to see the effect of this change.
To enhance the game further, it might be useful for the player to see how much time is remaining. Make a variable called Time left
	Insert a set [Time left] to [60] block just below the when Green Flag clicked block Insert a change [Time left] by [1] block into the forever loop before the if timer > 60 block
Insert a [ ] - [ ] Operators block into the second pane of the set [Time left] to [ ] block and edit the blocks so they read set [Time left] to [60] - [timer] The game is now more or less complete. You may want to play it a few times to see if you can maximise your score.
	You might want to add a High Score variable record the highest score. Here is one way which it could be programmed.