Block coding lesson 16: Variables: a box for a number
US version. US grades and US spelling. · UK version of this lesson
A variable is a named box that holds a number. set size to 3 puts 3 in the box called size. move forward size uses whatever number is in the box. A complete 40-minute block coding lesson (Grades 4–5), from Unit 6: Variables. Myrtle the Turtle runs right here in your browser – nothing to install.
- Time
- 40 minutes + 20 min homework
- Grade
- Grades 4–5 (ages 9–11)
- You need
- A computer or tablet, squared paper and a pencil
- Graded
- Instantly, with explanations
For parents: how to use this lesson
You don't need to know anything about coding. The lesson explains each step on screen, the way Mr Babbage, our Head of Computing, likes it: watch Myrtle first, then have a go. Programs are made from blocks – no typing – and every answer is graded straight away.
- Before the screen: Label a box "score", put counters in it and change them as you play a game.
- Press Start the lesson below and watch the worked examples together. Press Run and say what each block does before Myrtle does it.
- Let your child do the practice on their own. When Myrtle goes the wrong way, that's a clue, not a failure – press Run again and watch which block it is on.
- Finish with the talk question: “Why is a variable better than typing the same number four times?”
- Later that day or the next day: the homework (20 minutes), then a practice test.
Watch out for
- Thinking the variable remembers the first number for ever. A new
setreplaces the old number. - Typing the number instead of using the variable. Use the variable so the program works for every size.
Miss Lovelace's tip for home: ask your child to be Myrtle. Read out the blocks and let them walk it on the floor. If they can act it out, they understand it.
What your child will learn
Learning goal: set a variable and use it.
Success looks like
- I can set a variable and use it.
- I can say what a variable holds.
- I can write a program that works for any size.
Key words
variable · value · set · name
The big ideas (for the adult)
A variable is a named box that holds a number. set size to 3 puts 3 in the box called size. move forward size uses whatever number is in the box.
If the shape uses the variable everywhere, changing ONE block changes the whole picture. We test programs with other numbers in the box.
A worked example
set size to 4 move forward size turn right 90° move forward size
Press Start the lesson to watch the turtle run it.
The lesson, step by step
| Part | Time | How it is checked |
|---|---|---|
| Starter | 5 min | Graded by Classfern |
| Teach | 8 min | Watch, talk and try |
| Worked example and try it | 8 min | Graded by Classfern |
| Practice | 14 min | Graded by Classfern |
| Wrap up | 5 min | Graded by Classfern + self-check |
The lesson
It runs here on the page. No sign-up and no names – progress is kept only in this browser. Each visit picks a new mix of questions.
Homework
20 minutes: 6 questions – work out what Myrtle does, then build or fix a program – and a short reflection. New questions every time, all graded instantly. Away from the screen: label a box "score", put counters in it and change them as you play a game.
Practice tests
- Block Coding: Variables Practice Test (Grades 4–5)12 questions · graded instantly
- Block Coding: Mixed Practice Test (Grades K–5)15 questions · graded instantly
All computer science practice tests · All 18 block coding lessons
Curriculum
CSTA K–12 Computer Science Standards (2017), grades 3–5: 1B-AP-09 – Build programs that store and change data using variables; 1B-AP-10 – Build programs with sequences, events, loops and conditionals.
The standard codes are CSTA's; the descriptions are our own words.
Our lessons, blocks and questions are our own. They are not written or endorsed by any government department, testing agency or exam board.