Drawing with a turtle

Students meet the turtle, read a program that draws a digital 2, learn that the order of commands is the picture, and draw a 4 themselves.

Python Foundations with Turtle · Commands, loops and values · about 35 minutes · Open the student lesson

Classroom resources

Load these into Waypoints Prepare: choose Load URL and paste the copied address, or download the file and import it. In Prepare, the worksheet's Teacher edition shows the answers; the student copy hides them.

Slides Download Present from the browser, or export to PowerPoint or PDF.
Worksheet Download Print the student copy; the Teacher edition has the answers.

Students will be able to

I can say what forward, right and left do to the turtle.
I can say why the order of the commands matters.
I can write a program of several commands that draws a digit.

Timing

Meet the commands 8 min · Predict and Run 8 min · Put the lines in order 7 min · Make 12 min

Before class

Draw the 4 yourself. It takes two minutes, and you will see why the last turn is right(180).

Running the lesson

Meet the commands: you explain, at the board. Run the three lines live, one at a time. Say what forward and right do, that right does not move the turtle, and that left turns the other way.
Predict: show the digit-2 program and take a vote before anyone runs it. Ask students to walk it as the turtle. The wrong options are two slips: thinking the turns draw, and mixing up right with left.
Run: run it on the slide, then students run it themselves. Ask: which lines drew, and which only turned?
Put the lines in order: students do the ordering on their own screens. Circulate; if a student is stuck, ask which way the turtle is facing after the first turn.
Make: the 4. Hints are in the speaker notes. If the room is unsure, model the first stroke on the board and let students write the rest. The last stroke goes over a line already drawn, which is allowed.

In class

On the slides at these points. Students can do the whole lesson on their own; these are for the room. In the deck, the Run, Modify and Make slides have the live playground in them (the tutorial link is the backup), and the notes above are in each slide's speaker notes.

Think, pair, share (start)
A robot follows its commands in the wrong order and walks into a wall. Whose fault is it: the robot's or the programmer's?
- Did the robot do what it was told?
- What could the programmer have done to catch the mistake before running it?
Let students defend both sides. The robot did exactly what the program said, so the mistake is in the program. Return to this after the ordering task: did anyone's first order give a surprising picture?
By the end of this lesson (start)
Here is a digital 2 made from five lines of commands. By the end of the lesson you will write commands that draw a 4.

Show the finished 2 on the projector before anything else.
Play turtle (investigate, 5 min)
One volunteer is the turtle, standing in the middle facing the window. The class reads the commands aloud, one at a time. The turtle obeys: 3 steps for each forward, a quarter turn for right(90) or left(90).

Papert designed the turtle so learners could play it. Walking the commands makes it concrete that a turn changes which way forward goes.

The hard part (on purpose)

Remembering that right and left turn without drawing. Ask what the turtle did on that line, instead of telling them.

When students get stuck

What you will see	A question to ask	The fix
The turtle draws a line where the student expected a turn.	Does right(90) move the turtle, or only turn it?	right and left turn the turtle on the spot. Only forward draws.
The 4 comes out back to front, or the strokes point the wrong way.	Read the lines aloud in order, as if you were the turtle. Where does it face after each turn?	Each line happens after the one above it, and each turn changes which way forward goes. Swap a left for a right, or the other way, and see.
A NameError or "forward is not defined".	What is the first line of your program?	Every program starts with from turtle import *. Copy it to the top.

Answers to the checks

Predict: What will the turtle draw?
The digit 2. Five lines of 60, with a turn between each pair: across, down, across, down, across. The turns change direction without drawing (so not one straight line), and the first turn is right, so the turtle goes down on the right side first (so 2, not 5).
Put the lines in order: These five lines are mixed up. Put them in the order that draws the picture.
see the program below
The turtle goes across 60, turns left to face up, goes 40, turns right to face across again, then goes 60 more. Any other order draws a different picture, because each turn changes which way the next forward goes.
```
forward(60)
left(90)
forward(40)
right(90)
forward(60)
```

Solutions

One possible solution for each task. Other correct programs are fine.

Make

from turtle import *

right(90)
forward(50)
left(90)
forward(50)
left(90)
forward(50)
right(180)
forward(100)

Stretch and support

Stretch: Draw a second digit beside the first, such as an 8 or a 7. Where does the turtle have to start?

Support: Give the first stroke and the first turn, and ask the student to add the rest.

Exit ticket

A turtle runs forward(100), right(90), forward(50). How many lines does it draw, and which is longer, the first or the second?

Two lines (the turn does not draw). The first is longer: 100 steps against 50.

What each step is for

Put the lines in order: The order of the commands is the picture: the same lines in a different order make a different drawing.

Where it leads

Next lesson: the same commands again and again. A square is eight lines written out, and a loop makes it three.