Lesson 2 · Drawing Shapes

Module 1 · Learning to Drive

Lesson 2 · Drawing Shapes

50–60 minPhase A · Blockly FoundationBuild it up yourself

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Teacher mode is on — the gray boxes are yours only. This lesson is built as a discovery sequence: students figure out the square, and the shortcut, before either is explained. The gray boxes tell you what to hold back and when to reveal. Flip the switch (bottom-right) to preview the student view.

In Lesson 1 you drove the robot forward and back. Today you'll get it to draw a square — and you'll work out how, one block at a time. No recipe up front. Somewhere along the way you're going to invent a shortcut that programmers use constantly.

Learning Objectives

By the end of this lesson you will be able to:

• Build a program up one step at a time, running it after each change
• Make the robot trace a square, and explain why the program needs what it needs
• Find a shorter way to write a program that does the same thing many times
• Work out the turn angle for any regular shape (360° ÷ number of sides)

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Printable knowledge checks — the 6 questions from this lesson on one page, with room to write. Teachers: answer key.

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Clip — XRP driving a square on the floor

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Here's where you're headed. You'll get there one block at a time.

How to run this lesson (the whole point is who does the discovering)

Resist the urge to show the finished program. The sequence is: drive straight → add a turn → make a square with what you have → notice the repetition → find the shortcut. Students who arrive at "repeat the straight-and-turn four times" on their own own the idea of a loop; students who are handed the Repeat block have merely seen one. Your job is to ask questions, not answer them: "What did the robot do? What do you want it to do next? What's one block that would get you closer?" Budget roughly 10 min for straight + turn, 15 min for the square, 10 min for the shortcut, 15 min for other shapes.

Activity · Build up to a square

Three steps, each one a small change to the program you already have. Run the robot after every step — watching what it actually does is the point.

Step 1 · Drive straight

Open XRP Code and start a new project. Your first job is small: find a block that makes the robot drive straight for 20 centimeters. Look through the block palette, drag it out, and set it up. Put a Wait for button press block above it so the robot waits for you.

Upload it, set the robot on the floor, press the button. Did it go 20 cm? Roughly where did it end up, and which way is it facing?

Facilitating: Drive straight

Let students find the Straight block themselves — say "find a block that drives straight" rather than naming it. Most will spot it in seconds; the point is that they're searching the palette, which they'll need to do again when they hunt for the Repeat block. Expect a few to forget the button-press block and have the robot drive off the table — that's a memorable lesson about why the block exists. Keep this part short; it's a warm-up.

Step 2 · Add a turn

Now change your program so that after driving straight, the robot turns 90 degrees. Find the block that turns, add it under the Straight block, set the angle, and run it again.

Before you press the button, predict: where will the robot end up, and which way will it be facing? Then check.

Knowledge Check

Your program is Straight 20, then Turn 90. After it runs, how has the robot changed from where it started?

Facilitating: Add a turn

Ask "what shape has the robot drawn so far?" — a single side and a corner, an L. Then ask the leading question that sets up the square: "What would you have to add to draw a second side?" Don't answer it. Some students will already see where this is going. Good.

Step 3 · Make a square

Here's the real challenge: change your program so the robot drives a complete square and ends up back where it started, facing the same way.

You already know everything you need. Use the blocks you have. Try something, run it, watch what happens, adjust, run it again. It's fine if your first try is a triangle or an open box — that's information.

You've succeeded when the robot drives four roughly-equal sides, turns four corners, and finishes near its starting spot.

Facilitating: Make a square — let them build the long version

Nearly every student will solve this by stacking Straight, Turn, Straight, Turn, Straight, Turn, Straight, Turn — eight blocks. That is the correct answer for this part. Do not suggest the Repeat block; do not hint that there's a shorter way. If a student finds Repeat in the palette on their own and uses it, wonderful — ask them to hold on to it and demonstrate when the class gets to the shortcut.

Common stumbles: only three sides (miscounting), or a turn of 45° or 180° (they'll see a wrong shape and fix it — don't pre-empt). Once a student's square works, ask them to count their blocks and to point at anything that's repeated. That question is the bridge to the shortcut.

Once your square works, look at your program and answer these two questions:

1. How many blocks did it take?
2. Is there anything in it that's the same thing, over and over?

Knowledge Check

In the eight-block square, what is being repeated, and how many times?

Activity · A shorter way to say "four times"

You just wrote the same two blocks four times. Imagine drawing a shape with 12 sides — 24 blocks. There has to be a better way, and there is: the palette has a block that repeats whatever you put inside it. Go find it.

Drag it out, set it to run 4 times, and move one Straight and one Turn inside it. Delete the other six blocks. Run it. Does the robot still draw a square?

Facilitating: the reveal, after the search

Give students a minute or two to find the block themselves (it's Repeat in the Loops category). If someone found it while building the square, this is their moment to demonstrate. Only after most have tried it, show the finished version below and name it: this is a loop — one copy of the instructions, run as many times as you say. Emphasize the physical action of dropping blocks inside the Repeat's mouth — being beside it instead of inside it is the classic error, and the robot will show them (it drives one side and stops).

Once yours works, you've used a loop: you write the instructions once, and the Repeat block runs them as many times as you tell it to. That's one of the most important ideas in all of programming, and you got to it by noticing your own program repeating itself.

Knowledge Check

A student's Repeat-4 program makes the robot drive one side and then stop. What's the most likely problem?

Activity · Now try a triangle

Change your Repeat from 4 to 3. What angle should the turn be? Make your best guess, run it, and look at the result.

Facilitating: the triangle — let the wrong angle happen

Most students will leave the turn at 90° (the robot draws three sides of a square and stops, facing sideways) or guess 60° because they remember a triangle's corners are 60° — the robot then draws a wide, open zig-zag that never closes. Both failures are the whole point. Ask: "Did it close? Which way is it facing compared to the start? How far did it turn in total?" The move that makes the rule click: have a student walk the triangle, pivoting at each corner, and notice they've turned all the way around by the end — a full 360°. Three corners sharing 360° is 120° each. Only now go to the rule.

Didn't close? Before you read on, try this: walk the triangle yourself. Pace out a side, pivot at the corner the way the robot does, and keep going until you're back where you began, facing the way you started. How far did you turn in total, adding up all three corners? That total is the whole answer.

Now set your turn to the angle you worked out and run it again.

Knowledge Check

A classmate's triangle isn't closing up — the robot ends facing the wrong way. They used Turn 60°. What should it be?

Now do the reasoning on paper before you run anything else. Sketch a square and walk your pencil around it, writing the turn at each corner: four 90s that add up to 360. Then fill in the table for the rest:

Shape	Sides	Repeat	Turn angle
Triangle	3	3	____
Square	4	4	____
Pentagon	5	5	____
Hexagon	6	6	____
Octagon	8	8	____

Completed table (teacher copy)

Triangle 120°, square 90°, pentagon 72°, hexagon 60°, octagon 45°. Students who fill it in without the rule usually get the triangle wrong (60° instead of 120°) — that one row is the quickest check of whether the idea landed.

Collect the table if you want a paper artifact from this lesson; it's the only written work here.

Activity · Make other shapes

Now you can draw any regular shape by changing just two numbers — the repeat count and the turn angle. Use your table, predict the shape, then run it:

1. Pentagon — Repeat 5, and the turn angle from your table. Shorten the sides to 15 cm so it fits.
2. Hexagon — Repeat 6, and its angle from your table.
3. Your choice — pick a number of sides, work out 360 ÷ sides, predict the shape, run it. What happens as the number of sides gets big?

Check each one against your prediction before moving on: if the shape doesn't close, the angle and the repeat count disagree.

Knowledge Check

What turn angle do you need to draw a regular hexagon (6 sides)?

Knowledge Check

You change a working square program from Repeat 4 to Repeat 6, and set the turn to 60°. What does the robot draw?

Space, effort, and differentiation

Give each robot a clear patch of floor (about 1 m square at 20 cm sides). Lopsided shapes are usually wheel slip — lower Effort to 0.3 on carpet, or nudge to 0.7 if the robot is sluggish; within ~10% is a success. More support: a reference card of angles (3→120°, 4→90°, 5→72°, 6→60°, 8→45°) and a fill-in template "Repeat () · Straight () · Turn (__)." More challenge: a five-point star (Repeat 5, Turn 144°) — ask them to work out why 144 before running it — or two shapes back-to-back from the same start.

Real-world connections

Repeating a move-and-turn is exactly how machines make precise, repeatable paths:

Manufacturing

CNC machines

Cutting tools trace shapes by repeating precise move-and-turn steps, just at much finer scale.

Making

3D printers

Each layer is a looped path the print head repeats hundreds of times to build up an object.

Art

Pen plotters

Drawing robots turn loops of coordinates into logos, maps, and signatures on paper.

Wrap-up

• Why did the eight-block square work, and why is the Repeat version better? (Same result; one copy of the instructions instead of four, and easy to change.)
• What's the rule for the turn angle? (360 ÷ number of sides.)
• If a shape doesn't close, what's the first thing to check? (The turn angle — did the turns add up to 360?)

Assessment & next lesson

Formative: did each student get a square working before seeing Repeat, and can they say what the Repeat block does in their own words? Can they state the repeat count and angle for a named shape? Exit ticket: "Octagon — what goes in the Repeat, and what's the turn?" (8, 360 ÷ 8 = 45°). Preview: next lesson we take this square code and tuck it inside a function so we can reuse it by name — and, true to form, students will feel the need for one before they meet it.

Resources

• XRP Code IDE
• XRP Robot User Guide