One question I often get about problem-based lessons is “What should I do if students finish a problem early?” The conversation often shifts to ways to extend the problem so that students who are done and want more challenge have something to do. So in this blog post I want to dive into a distinction between two types of extensions: depth and breadth.

For this example, let’s pretend that your students have been working on my In-N-Out 100×100 Cheeseburger problem. Some students are done with the problem while others need more time. Here is my understanding of what depth and breadth extensions might look like in this situation.

Depth
Depth extensions tend to use the same context but use more advanced math skills to solve the problem. For example, after students find the cost of a 100×100 burger, you could ask students to figure out how big of a burger they could order with the money they have, write a formula for when you want different amounts of meat and cheese, or solve the problem again using a different method.

Note that in this case, the context has not changed (they’re still working with the cost of the burger) but students now have to use slightly different mathematics and solve a related problem.