KS1 Pizza pickle debugging activity page 1/12

Recommended Year Group: Year 1 & 2 (can be adapted for other years)Activity Duration: 1 hour

Concepts and approaches

Programming PerseveringDebugging Logic

Curriculum linksComputing• debug simple programs• use logical reasoning to predict the behaviour of simple programsCooking and nutrition (Design and technology)• use the basic principles of a healthy and varied diet to prepare dishes

IntroductionIn this activity pupils will be given programs that do not do as expected and will be asked to fix them. In doing this they are using logical reasoning to predict what will happen and debug.

Prior knowledge Pupils should already have an understanding of algorithms and have programmed simple activities in Scratch. This could be through completing:• Crazy characters or another introduction to algorithms activity• Scratch tinkering• Scratch bot programming UK map (coming soon) or another introduction to programming activity

Pupil objectives• I can debug a Scratch program.• I can say what a program will do.• I can explain what the bug was and how I fixed it.

Resources• MIT’s Scratch 2.0 or Scratch 1.4. If possible please use Scratch 2.0, as the

purple 2.0 command blocks are much easier to read than the yellow broadcast commands used in 1.4. (Please refer to this guide on the ways to download or use our Scratch resources in your school)

• Pupil access to Scratch, in pairs, and project Scratch resources – either down-loaded from Pizza Pickle.sb2 (2.0) or Pizza Pickle.sb (1.4) or use within the Scratch 2 online editor from this link: Pizza Pickle Online 2.0

KS1 Pizza Pickle ActivityAn introduction to debugging Scratch programs

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• Whiteboard for writing up pupils’ ideas about debugging• An interactive whiteboard to display Scratch as you work through this lesson• Pizza Pickle teachers’ presentation 2.0 or Pizza Pickle teachers’ presentation 1.4

(see download link at bottom of webpage)• Pizza Pickle Orders Worksheet 2.0 or Pizza Pickle Orders Worksheet 1.4 (see

download link at bottom of webpage)• Pizza Pickle Helpsheet. 2.0 or Pizza Pickle Helpsheet 1.4 (see download link at

bottom of webpage)

Before you start• Download the Pizza Pickle file appropriate to your version of Scratch and save

to a location on your network for pupils to access, or ensure they have access to Scratch 2 online.

• Print out and photocopy the Pizza Pickle Orders of programs with bugs (one per child)

• Print and give out and photocopy Pizza Pickle Helpsheet (one per pair)• Read the Teaching Notes - concepts and approaches on page 10.

OrganisationPupils will need access to Scratch 1.4 or 2.0. This activity is most effective if using using Scratch 2.0. Ideally, pupils should work in pairs for this – it’s probably best to partner less confident coders with those who are more confident with Scratch.

Introduction whole class (5 - 10 mins)• Bring children to the carpet.• Show children the commands page of the presentation as below. Ask pupils what

they think they will be programming and what programming language the activity might be created in. (Answer – making pizza using Scratch)

Version 2.0 and 1.4

• Open the Pizza Pickle scratch file. You might find it useful to revise the areas for scripting, pointing out to the pupils the steps they need to go through to find the block they will be using. See the images below for these steps. If needed use the slides below to remind children after you have walked this through, or use them as helpsheets.

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Version 2.0 This image is included in the helpsheet.

Version 1.4 This image is included in the helpsheet.

• Make sure that pupils can access the pizza pickle commands (see image above).• Ask them what the different commands might do and how we might use them.

But most importantly how we can find out. Lead them to the idea that they could tinker. Explain we are going to focus on finding out about the special purple commands (2.0) or broadcast message commands (1.4) not the rest of Scratch today.

• Remind them of the areas; the stage area (where they will see the output from

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the program), the blocks palette (More Blocks) (in 2.0) (where they can get the pizza commands from), the scripts area (where they will write their program).

Tinker time (10 mins)• Demonstrate how your pupils will access the program by clicking on the down

loaded Pizza Pickle file. Show them how to click on ‘File’, ‘Save As’ and save as a sensible file name in an area on the school network so that each pair will have their own version of the project file e.g. Sam Chloe Pizza (unless pupils are working with their own Scratch online accounts).

Selecting ‘File’ then ‘Save as’ in Scratch 2 and 1.4 to save a copy of the project.

• If your class needs this, or for those requiring extra support, show them how to click on the commands to run them and how to snap the commands together.

• Show them how to use the help sheet if they get lost.• Show them how to quit and re-open the pizza pickle file if they get in a pickle!• Give pupils 5 minutes to tinker with the program.• During this time, encourage pupils to try the pizza commands. Ask them to click

on each block and see what it does. Ask them what surprised them, what it can or cannot do. Ask pupils to demonstrate to others what they find out.

• In Scratch 2.0 remind children to click on ‘More Blocks’ if they get lost in the Blocks palette.

Introduction to debugging (10 mins)• Return children to the carpet.• Ask children to discuss with a neighbour what they found out and then discuss

as a class. Children could show their discoveries on the IWB by demonstrating what the commands do and how they work. Ensure that all the commands have been explored.

• If necessary use the Programming Commands page of the IWB as shown below (slide 4), or the Pizza Pickle Helpsheet or click on each command to show them. (Remember to click on green flag after you have run each command to clear the stage).

.

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Version 2.0 This image is included in the help sheet

Version 1.4 This image is included in the help sheet.

• Ask pupils what they think a bug in a program is. Explain it is when we want a program to do something but it does something different.

• Ask pupils what they think debugging is. Explain if there is a bug then getting rid of it is called debugging.

• Explain that bugs are a common thing when we program. Even professional programmers have to debug. Often half of the time they spend programming is spent debugging, so we have to get used to doing it too!

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• Share the learning intention page, if this is your normal practise.

Please adapt to your schools format, if used.

• Explain there are some pizza orders for the pizza shop, but the programs are in a pickle – they have gone wrong. What do we call it when the program does not do as we expect? It has a bug in it – we need to debug.

• Explain that sometimes it’s helpful to have steps to help us debug. (Don’t worry if they don’t remember these – they will gradually grow to remember them as you remind them continually and they are on the Pizza Order Worksheet!). We work out…

• What should it do?• What does it do?• Where does it go wrong?• Fix it.

• Show them the next slide and read out what the program should do and then ask the pupils to work out with their partners what they think the program will do. Take ideas from the class and address any misconceptions by modeling how to look at each command and talk through what you think it will do and therefore what the program will do. (Some children may say it will be fine, others may spot it has not been cooked, or that it has no topping it is important for pupils to pre-dict, rather than being told what will happen at this stage.)

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Plain pizza order version 2.0

Plain pizza order version 1.4

• Show children how once you have predicted what will happen, how it can be tested. Click the green flag to show you are clearing the stage.

• Then snap the commands together and click on them to run them.• Model clearly talking through where the bug is, modelling the use of logical think-

ing. Saying something like “So it makes the base, there is the oven – but it’s still in the oven, what command do I need to get it to cook. There is a ‘start cooking’ – maybe I need to add that at the end, lets try it’.

• Demonstrate testing what the original buggy code does. Then demonstrate fixing it. Drag the extra command ‘start cooking‘ and snap to the end of the sequence. Press green flag to clear the stage and re-test by clicking on the new program

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you made. Talk through it and say yes a plain pizza with no toppings.• (This may seem like overkill, modelling these debugging steps for such a simple

bug, but it is well worth getting children into the habit of thinking through the de-bugging steps as habit, it will help enable them to be more independent as they move onto creating more complex programs and therefore fixing their own bugs.)

Purposeful programming (30 mins)• Show the children the Pizza Pickle Order Worksheet as below.

Pizza pickle order worksheet version 2.0

Pizza pickle orders worksheet version 1.4

• Show them how you filled in the plain pizza row (just jot the new commands in the fix it column).

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• Show them the next pizza order and the buggy program to make the order. Ask them what they think it will do? Where do they think it goes wrong? Those who are confident to have a go, send them off to predict what is wrong, to snap the commands together to write the buggy code, test it and then fix it (debug).

• For those that need more modelling, walk through the process for next pizza order. Look at each command, what will it do? Where does it go wrong. The most important thing is to keep returning to the debugging steps.

• What should it do? Make 1 pizza with sauce.• What does it do? Makes a pizza with cheese.• Where does it go wrong? There is add cheese.• Fix it. Change the add cheese command to add sauce.

• In the end they will learn by doing, they just have to have a go and persevere. Some will find this harder than others, those with an attention to detail and pa-tience may find this easier than those who expect to know straight away. But they all need to learn for themselves.

• Ask pupils to explain the steps they use to debug the sets of commands and get them to share with the class any clear explanations where they have followed the debugging steps e.g. I knew it had to make a cheese pizza but the program added basil so that is where it went wrong so I got rid of that command and it worked.

• If pupils finish the example buggy programs they can write in their own pizza order, get their partner to create a program with a bug, then get the person who raised the order to work out what the buggy program will do and fix it. They might also work collaboratively to help other pairings who are struggling. Or they could investigate how the the pizza pickle blocks / commands work and report back to the class what they find (See Teaching Notes - Programming on page 11).

Plenary (5 mins)• Ask pairs to share with another pair which was the hardest bug to fix and why.

Share ideas.• Share any buggy programs that children have created during the main task and

see if you can fix them as a class or make up one for them to fix e.g I want a bas-il pizza but the program was make base, add basil, add cheese, start cooking.

• Explain to children that almost always there are bugs in programs, bugs are not a problem, they are just something that happens when we program. People who can find bugs are great programmers. Suggest a bug finder display, or sticker or award. Only those who can find bugs have any chance of fixing them. Pupils could start a programming journal where they jot down ideas and bugs they found.

DifferentiationSupport:• Consider mixed pairing for less confident pupils to be supported by their peers,

however ensure that the more confident of the pair works collaboratively being supportive rather than taking over the task. An additional adult, if available, could work with a small group of pupils requiring additional support.

Stretch & Challenge:• Pupils can be challenged to clearly explain every step of the how they have

debugged a program and to support others in debugging. However be very mindful to train them to work collaboratively and to ask their peers the debugging

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steps, rather than giving their peers the answers!• Pupils could also investigate the pizza pickle programming language. In the

2.0 version they can look at the code that defines the custom blocks, this can be found at the bottom of the ‘make pizza’ scripts area, or in 1.4 they can trace through the broadcast commands.(See Teaching Notes - Taking this further on page 12.)

Assessment opportunities• A selection of open questions have been provided throughout to help encour-

age and gauge pupils’ developing understanding of debugging simple programs. Pupils who work out what the program should do, what it does do, where it goes wrong and then fix it are making good progress. Pupils who look at each com-mand in turn and explain their thinking are making good progress. Pupils who haphazardly try changing things with no reason are not making such good pro-gress, even if they fix the bugs!

• Pupils record their learning on their handouts – these can be marked.• The following questions can be used to assess progress and encourage a logical

approach to debugging:• What should it do? Show me where it tells you.• What does it do? How do you know that?• Where does it go wrong? Show me how you know that.• Have a go at fixing it yourself.

Teaching NotesAlternatives to ScratchScratch is not the only visual programming language that can be used for this activity. Scratch Jnr, Hopscotch, Kodu or other visual environments can be used. If an alternative language is chosen then a program needs to be prepared that requires debugging.

Concepts and approaches

DebuggingThe process of detecting and correcting the errors in a program is called debug-ging. Bugs happen in programs all the time and therefore debugging is an impor-tant skill to have. In this activity as pupils construct the program they are encour-aged to constantly test it, after they add each new commands and debug it if an error has occured.

Pupils are debugging when they take the sets of commands and work out:• What should it do? • What they do• Where they go wrong• Fix them

You could make up actions for debugging steps and share on the Barefoot web-site. You could make a class poster of these steps and as you find out more about debugging add extra notes, perhaps have a bug of the week and give stickers to

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It is particularly important skill for children to learn that they decompose their prob-lem into parts, and program a part, debug it, and then add the next set of steps. Giving pupils challenges with intermediate stages is a great way to encourage decomposition and debugging as you go skills.

ProgrammingProgramming is the act of purposefully combining commands in a programming language to create a program to solve a problem. The pizza pickle programming language has been written in Scratch just for this activity. This special pizza pickle language only has a few commands and how it works (the syntax) is very simple.

The Scratch 1.4 version of the pizza pickle programming language uses yellow broadcast blocks to create the pizza pickle commands. Whereas in 2.0, purple custom blocks have been used to create the pizza pickle commands. Custom blocks are not available in 1.4.

Version 2.0 allow coders the opportunity to create new blocks (the purple ones) in the ‘more blocks’ pallet. This allows us to hide the complexity of what is ‘inside’ these blocks from the person using them.

If pupils delete the yellow broadcast commands in the 1.4 version it is probably easiest if they close the pizza pickle file and start again by reopening the original file. But if they are using version 2.0 pupils can find the ready customised blocks in the purple ‘more blocks’ pallet.

As an extension, perhaps suited to more confident pupils and teachers, how the custom blocks work in 2.0 can be investigated, as can how broadcasts work. In actual fact the custom blocks in 2.0 just hide broadcast commands. For example, the blocks used in the 2.0 version of Pizza Pickle were simply copied from the 1.4 version. The custom blocks in 2.0 are defined on the make pizza script area at the bottom, just scroll down on the stage area to reveal the following..

Version 2.0 of pizza pickle uses custom blocks to hide the broadcast commands.

To investigate the broadcast commands, in 1.4 or 2.0, click on the different sprites to see where the broadcasts are raised or waited for. How broadcasts work is looked at in more detail in activities such as KS2 dinosaur fossil animation. Per-haps pupils could create their own blocks to add their own favorite toppings, such as mushrooms or pineapple?

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LogicWhen pupils predict what the sets of commands will do they are using logical reasoning to think what they have seen the commands do before and apply this knowledge to the problem in hand. It is important to encourage pupils to explain their thinking, this not only shows whether they are thinking logically, but also helps them to think through their own ideas. Being able to explain what we think a program will do is very important not only when we first create a program but also when we debug it.

PerseveringPersevering means being determined, resilient and comfortable with not knowing the answer and having to work on a solution for some time. When solving prob-lems there may be many alternative solutions, sometimes it is not clear which is the best until you have tried them, so pupils may have to try out a number of alter-natives to better able to compare them.

Taking this furtherBBC What are computer bugshttp://scratched.gse.harvard.edu/resources/debug-ithttp://wiki.Scratch.mit.edu/wiki/Debugging_Scripts

Related activitiesLower KS2 Fossil formation sequencing activityKS2 2D Shape Drawings – an introduction to debugging algorithms