Lesson 2 of 5 · HDB Void Deck

Loops: a 45-minute coding lesson

A free 45-minute lesson on loops for ages 6–12. Students use "repeat" to water every plant along an HDB void deck corridor in a few blocks.

  • 45 minutes
  • Pairs, whole class
  • One device per pair, plus a projector
Open level 1

Learning objectives

By the end of the lesson, students can:

  • Recognise a pattern of instructions that repeats.
  • Use a repeat loop to replace a long sequence of the same blocks.
  • Put a loop inside another loop (a nested loop) to cover rows.

Key words

Loop:
An instruction that repeats other instructions.
Repeat:
Do the blocks inside a set number of times.
Pattern:
Something that happens again and again in the same way.
Nested loop:
A loop inside another loop.

You'll need

  • One laptop, Chromebook or iPad per pair, open to dotcodecampus.com/maze/void-deck/1. No accounts or installs.
  • A projector or screen for the demo.
  • Optional: the printable unplugged grid game for the warm-up, and certificates to finish.

Lesson flow

  1. Minutes 0–8

    Unplugged warm-up

    • Clap a rhythm: clap, clap, stomp, clap, clap, stomp, clap, clap, stomp. Ask students to write it down.
    • Compare the long version with "repeat 3 times: clap, clap, stomp". Which is quicker to write? Which is easier to change to 10 times?
    • Introduce the word loop.

  2. Minutes 8–15

    Demo on the projector

    • Open HDB Void Deck level 1 (dotcodecampus.com/maze/void-deck/1). Count the squares to the lift together.
    • First solve it with nine "move right" blocks, then show the one-block loop. Compare the star ratings.
    • Click "Show me the Python" to show that a loop in Python is written "for i in range(9):".

  3. Minutes 15–35

    Paired play: levels 1–6

    • Pairs work through levels 1–6, swapping driver and navigator at each level.
    • Before building, ask pairs to say the pattern out loud, e.g. "right, water, right, water…".
    • Level 6 needs a loop inside a loop. Suggest solving one row first, then wrapping it.
    • Three stars on every level unlocks the bonus "Corridor Marathon".

  4. Minutes 35–42

    Class discussion

    • How did you spot the part that repeats?
    • Why do programmers like loops? (Shorter code, fewer mistakes, easier to change.)
    • What loops do you see in daily life? (Seasons, a washing machine cycle, school timetable weeks.)

  5. Minutes 42–45

    Exit ticket

    • Rewrite "right, right, water, right, right, water, right, right, water" using a repeat block.

Early finishers: Design a corridor where the plants need a nested loop, and challenge a partner to solve it in the fewest blocks.

Answer key

One three-star solution per level, in Python. Other solutions with the same number of blocks earn three stars too. Jump links take the class straight to a level.

Level 1: To the Lift

2 blocks

dotcodecampus.com/maze/void-deck/1

for i in range(9):
    move_right()

Level 2: Thirsty Plants

3 blocks

dotcodecampus.com/maze/void-deck/2

for i in range(5):
    move_right()
    water()

Level 3: Every Other Pot

4 blocks

dotcodecampus.com/maze/void-deck/3

for i in range(4):
    move_right()
    move_right()
    water()

Level 4: Staircase

4 blocks

dotcodecampus.com/maze/void-deck/4

for i in range(4):
    move_right()
    move_down()
    water()

Level 5: There and Back

7 blocks

dotcodecampus.com/maze/void-deck/5

for i in range(4):
    move_right()
    water()
move_down()
for i in range(4):
    move_left()
    water()

Level 6: Snake Walk

9 blocks

dotcodecampus.com/maze/void-deck/6

for i in range(2):
    for j in range(3):
        move_right()
        water()
    move_down()
    for j in range(3):
        move_left()
        water()
    move_down()

Bonus: Corridor Marathon

4 blocks

dotcodecampus.com/maze/void-deck/bonus

for i in range(4):
    for j in range(3):
        move_right()
    water()