🧩 Break It into Parts, Then Break It on Purpose v0.1.0
Students split a big job into small parts that are each obviously right, then try to break a number machine with the oddest input they can think of. These are decomposition and testing, the two habits that make programs work.
You will need
- The printable's planning sheet and rule cards
- Pencils
- Chart paper for the class number machine
The lesson, step by step
Pick a big job
Write on the board: "Put on a class show." Ask: "Can we do this in one step?" Of course not. Ask groups to break it into five or six parts, and then break each part into smaller ones until each is something a person could just do.
Check the parts
A good part is small enough to be obviously right. Groups read their parts aloud and the class votes: "Could someone just do this one without asking another question?" Parts that fail get split again.
Put the parts in order
Some parts must come first and some can happen at the same time. Groups number their parts and circle the ones that can happen at once. This is how a team splits a job among people, and how programmers split a program into functions.
Meet the number machine
Show a rule card: "The machine takes a number, doubles it, and adds 1." Test with 3 (7) and 10 (21). Ask which numbers the machine hasn't been tried on yet.
Try the weird case
Groups hunt for the oddest input they can think of: 0, a very big number, a negative number, a number with a point in it, nothing at all. For each one they predict, then test it by working it out. If the machine does something odd, they have found a weird case.
Write a test list
Each group writes five tests for its rule card: two ordinary, two odd and one on the edge. They share the one most likely to break a rule. Say that this is what testers do for a living.
Questions to ask while they work
- Could someone just do this part?
- Which part has to come first?
- What is the oddest thing you could give the machine?
- What did you expect, and what happened?
If it goes fast
- Write a rule that has a weird case on purpose, and let another group find it.
- Break the show plan into jobs for a real small class event.
- Decide which test would be the most important if you could only run one.
The printable
Cut the rule cards apart. Each group needs one rule card, the planning sheet and the test list.
🧩 Parts planner, rule cards and test list
Name: ______________________
- Double it, then add 1
- Take away 3, then double it
- Add 10, then halve it
- Square it, then take away 1
- If it is more than 5, add 2. Else take away 2.
- Count down from the number to 0 and add them
- Skip count by 2 from the number
- Take the number and say it three times
Parts and tests
1. Our big job: ______. Write the parts in the order we do them.
2. Our rule card: ______. Write five tests: two ordinary, two odd, one on the edge. For each, write what you expect and what you got.
◂ The Scoreboard Game · All ten lessons · Read It, Run It, Say It ▸
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