Lesson 3 of 5 · MRT Station

Conditions: a 45-minute coding lesson

A free 45-minute lesson on conditions (if / else) for ages 7–12. Students teach a robot to wait for MRT fare gates and train doors.

  • 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:

  • Explain that a condition lets a program choose what to do.
  • Use if / else to react to something that changes, like a gate opening.
  • Combine a condition with a "repeat until" loop.

Key words

Condition:
A question with a yes or no answer, like "are the doors open?".
If / else:
If the answer is yes, do one thing; otherwise, do another.
Repeat until:
Keep repeating until something is finished.

You'll need

  • One laptop, Chromebook or iPad per pair, open to dotcodecampus.com/maze/mrt/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

    • Play "Traffic Light": students walk on the spot when you hold up green and freeze on red.
    • Write the rule on the board: if the light is green, walk; else, wait.
    • Ask: could you have known the colours in advance? Why is a rule better than a fixed plan?

  2. Minutes 8–15

    Demo on the projector

    • Open MRT Station level 1 (dotcodecampus.com/maze/mrt/1) and watch the doors open and shut before running anything.
    • Solve it by counting "wait" blocks, then open level 3 and show how an if / else inside "repeat until finished" works no matter the timing.
    • Show the Python: "while not finished():" and "if door_open():".

  3. Minutes 15–35

    Paired play: levels 1–6

    • Pairs work through levels 1–6, swapping roles at each level.
    • The gate and door chips under the board show whether they are open. Ask pairs to watch them while the robot runs.
    • Level 6 needs one if inside another. Ask: what two questions must both be true before the robot moves?
    • If a pair is stuck, use the Step button to go through the program one block at a time.

  4. Minutes 35–42

    Class discussion

    • Why is "if the gate is shut, wait" better than counting waits?
    • What would happen at a real MRT station if the doors had no sensors?
    • Where do you see if / else around you? (Automatic doors, lift buttons, a game checking if you pressed jump.)

  5. Minutes 42–45

    Exit ticket

    • Finish the rule: "If it is raining, ___; else, ___." Then write a robot version for the train doors.

Early finishers: Write if / else rules for a school canteen queue robot: what should it check before moving forward?

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: Mind the Doors

7 blocks

dotcodecampus.com/maze/mrt/1

move_right()
move_right()
wait()
wait()
wait()
wait()
move_right()

Level 2: Long Platform

2 blocks

dotcodecampus.com/maze/mrt/2

while not finished():
    move_right()

Level 3: Doors Open?

4 blocks

dotcodecampus.com/maze/mrt/3

while not finished():
    if door_open():
        move_right()
    else:
        wait()

Level 4: Fare Gates

4 blocks

dotcodecampus.com/maze/mrt/4

while not finished():
    if gate_closed():
        wait()
    else:
        move_right()

Level 5: Down to the Platform

6 blocks

dotcodecampus.com/maze/mrt/5

move_down()
move_down()
while not finished():
    if door_open():
        move_right()
    else:
        wait()

Level 6: Rush Hour

6 blocks

dotcodecampus.com/maze/mrt/6

while not finished():
    if gate_closed():
        wait()
    else:
        if door_open():
            move_right()
        else:
            wait()

Bonus: Last Train Home

8 blocks

dotcodecampus.com/maze/mrt/bonus

move_down()
move_down()
while not finished():
    if gate_closed():
        wait()
    else:
        if door_open():
            move_right()
        else:
            wait()