Recursion: A Function That Calls Itself
Python Programming 2 Grades 9–12 2-day lesson 21 deliverables Teach students how a Python function can solve a problem by calling itself on a smaller one. Students trace a stack of calls on paper, find base cases and see how the answers come back up one call at a time. They write a countdown function that calls itself, add the base case a recursive sum is missing and fix a factorial function.
● Instant download · Lifetime access · Editable & print-ready
Print + digitalPDF, PowerPoint, Word & Google
Answer keysA key for every page
Built-in assessmentExit tickets + lesson quiz
45-minute daysEvery day planned and timed
Short coding levels practice this lesson in CodeGrove, our code lab that runs in the browser. Students write the program, run it and check it, with no account and nothing to install. Use them with the lesson or as practice later.
See the levelsWhat does this lesson cover?
A function that calls itself can feel like magic, and a missing base case ends with a RecursionError. This lesson draws the calls as a stack, so students can see each call wait for the one below it.
The try-it on Day 1 and the quiz task on Day 2 run online in CodeGrove, our in-browser code lab, so students need a computer or tablet on those days. The 6.4 Try It level practices writing a countdown function that calls itself and adding the base case a recursive sum is missing. CodeGrove is free, with no accounts, sign-ins or installs.
Stack of Calls
Students trace a stack of calls and find base cases on paper with computers closed.
Everything that's included
00 Start Here
- READ FIRST: every file in the lesson and when you use it
- Teacher Guide and Pacing: the plan for each day, what to print and how to grade
- Skills map: which standards each day teaches
01 Present
- One editable PowerPoint deck for both days, 17 slides, with speaker notes
- Slide script: the speaker notes, printed
- Bell ringers: a short warm-up for each day
02 Student Handouts
- Guided notes: one packet for both days, in PDF and editable Word. Students fill in the blanks during the slides, with the word bank on the page
- Vocab slip: the lesson's words and what they mean, on one page
04 Activities
- Stack of Calls: students trace a stack of calls and find base cases on paper with computers closed
- Quiz task: students fix two bugs in a recursive function in CodeGrove, working alone, and then take the lesson quiz on paper
05 Assessment
- Exit tickets: quick questions that show who needs more help
- Lesson quiz: 8 multiple-choice questions and 2 written answers about both days, on paper
06 Answer Keys
- 4 answer key files: a key for each day (its bell ringer, notes and exit ticket) and the activity keys, plus the quiz key
Digital: Google Forms™ + Google Slides™
- 3 Google Forms™ of the exit tickets and the quiz, ready to copy into your Drive
- The multiple choice grades itself, and you grade the written answers
- A Google Slides™ copy of the deck, with the same slides and speaker notes, for Google Classroom™
- Give a Form that asks students to read code only on school-managed Chromebooks in locked mode, and use the paper version on other devices
Online: CodeGrove
- In CodeGrove: the quiz task on Day 2, on a computer or tablet for each student
- A try-it on Day 1: students practice the new code in CodeGrove, and nothing is turned in
- Free to use, with no accounts, sign-ins or installs
Why teachers love this lesson
A base case stops the callsStudents find the base case that answers the smallest problem and the recursive case that moves toward it.
Each call waits for the call below itTracing the stack on paper shows how the answers come back up one call at a time.
Print and digitalEvery page is a print-ready PDF, and the Google Forms™ and Google Slides™ let you teach the same lesson in Google Classroom™.
Real online labsStudents write and run real Python in CodeGrove, our in-browser code lab, on a computer or tablet, with no accounts or installs.
A key for every pageEvery day has its own answer key, and every written question has a sample answer and what to look for.
Every day fits a 45-minute classEach day's plan is timed activity by activity against real reading and writing speeds.
What Teachers Say
Be the first to review this
Reviews help me a lot, and they help other teachers pick the right resources for their classes. It takes about a minute.
Leave a reviewQuestions teachers ask
How do I get the files after I buy?
Instant download right after checkout: PowerPoint and Word files you can edit, print-ready PDFs, and links that copy the Google Forms™ and Google Slides™ into your Drive.
Can I buy the whole unit or course instead?
Yes. This lesson is part of the Unit 6 bundle and the complete Python Programming 2 course. Both cost less than buying the lessons one at a time.
Is this AP Computer Science?
No. It is a full-year, non-AP second course in Python for grades 9 to 12. For AP, see our AP Computer Science A and AP CSP courses.
What should students know before this lesson?
Students know parameters, return, and if and else, and they can read an error message's name and line.
Do students need computers?
Yes, on the CodeGrove days. Each student needs a computer or tablet that's online, and CodeGrove needs no account or install. The bell ringers, notes, exit tickets and quiz are on paper.
What formats are the files in?
Every page is a print-ready PDF. The slides are an editable PowerPoint and the guided notes an editable Word file. The exit tickets and the quiz also come as Google Forms™, and the deck as Google Slides™.
Which standards does it cover?
Written for Florida's Intermediate Programming course (9007220). The skills map in the lesson shows which standards each day teaches.