Lesson 7: Nested Loops

Nested Loops | Loops


In this online activity, students will have the opportunity to push their understanding of loops to a whole new level. Playing with the Bee and Plants vs Zombies, students will learn how to program a loop to be inside of another loop. They will also be encouraged to figure out how little changes in either loop will affect their program when they click Run.


In this introduction to nested loops, students will go outside of their comfort zone to create more efficient solutions to puzzles.

In earlier puzzles, loops pushed students to recognize repetition. Here, students will learn to recognize patterns within repeated patterns to develop these nested loops. This stage starts off by encouraging students try to solve a puzzle where the code is irritating and complex to write out the long way. After a video introduces nested loops, students are shown an example and asked to predict what will happen when a loop is put inside of another loop. This progression leads into plenty of practice for students to solidify and build on their understanding of looping in programming.


Warm Up (10 min)

Main Activity (30 min)

Wrap Up (15 min)


Students will be able to:

  • Break complex tasks into smaller repeatable sections.
  • Recognize large repeated patterns as made from smaller repeated patterns.
  • Identify the benefits of using a loop structure instead of manual repetition.



Heads Up! Please make a copy of any documents you plan to share with students.

For the Teacher

For the Students


  • Loop - The action of doing something over and over again.
  • Repeat - Do something again


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Teaching Guide

Warm Up (10 min)


Briefly review with the class what loops are and why we use them.

  • What do loops do?
    • Loops repeat a set of commands. (see vocabulary on command if students don't recognize it)
  • How do we use loops?
    • We use loops to create a pattern made of repeated actions.

Tell the class that they will now be doing something super cool: using loops inside loops. Ask the class to predict what kinds of things we would be using a loop inside of a loop for.

"If a loop repeats a pattern, then looping a loop would repeat a pattern of patterns!"

Students don't need to understand this right away, so feel free to move on to the online puzzles even if students still seem a little confused.

Main Activity (30 min)

CSF Express Course - Website

We highly recommend Pair Programming - Student Video in this lesson. This may not be an easy topic for the majority of your students. Working with a partner and discussing potential solutions to the puzzles might ease the students' minds.

Also, have paper and pencils nearby for students to write out their plan before coding. Some puzzles have a limit on the number of certain blocks you can use, so if students like to write out the long answer to find the repeats, paper can be useful.

Wrap Up (15 min)


Having students write about what they learned, why it’s useful, and how they feel about it can help solidify any knowledge they obtained today and build a review sheet for them to look to in the future.

Journal Prompts:

  • What was today's lesson about?
  • How did you feel about today's lesson?
  • What is a nested loop?
  • Can you draw a puzzle that would use a nested loop? Try coding the solution to your own puzzle.

Standards Alignment

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CSTA K-12 Computer Science Standards

AP - Algorithms & Programming
  • 1B-AP-11 - Decompose (break down) problems into smaller, manageable subproblems to facilitate the program development process.