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Writer's pictureLindsey Gallas

What's the Main Idea?

Over the past two years we’ve worked with many teachers and schools to help them implement the Math Medic lessons as their primary high school curriculum. The conversations we’ve had with teachers have been so insightful for us. We’ve heard about successes from teachers but we’ve also heard about the challenges. One such challenge is that it can be hard to teach a lesson that you didn’t write yourself. We totally agree!


Teaching a lesson that was developed by someone else requires the teacher to plan differently than they would if they had created the lesson themself. When creating your own lesson, you are the one who sets the goal of the lesson. You know where students are starting and where you want them to end up. You understand the progression of the questions and how you’re going to guide students along. This helps you more effectively monitor group work and facilitate the debrief because you understand how the thinking is being developed and the big idea you want students to land on.


So how can we plan efficiently and effectively to teach a lesson we didn’t create? The most important thing to do when prepping for a lesson is to identify the main idea of the lesson. This may seem obvious, but there is such value in zooming out from the individual questions in an activity and thinking about the lesson from a more holistic view. When we are talking about the main idea of the lesson, we’re talking about more than just the lesson title. We want to identify the main idea that we want students to understand. If you could only pick one thing that students take away from the lesson, what would it be?


To identify the main idea, the first step is to work through the lesson as a student would. This will give you valuable information about how the questions build on each other to develop students’ conceptual thinking. Once you’ve worked through the activity, identify the main understanding that you want students to take away from the activity. We use the Lesson Planning Guide to log this. We also identify which questions in the activity are most important. This helps you to keep your debrief focused on the most important parts. This is especially helpful if you’re short on time in a class period.

Let’s look at how this works with Lesson 5.5: Logarithms from Algebra 2. While the title of the lesson communicates that we obviously want students to learn about logarithms, we need to identify exactly what we want students to know about them. After working through the activity as a student, you’ll notice that the key understanding that we want students to take away from this lesson is an understanding that a logarithm gives an exponent as an output and the relationship between exponents and logarithms.


Having a clear main idea will help you to monitor groups and lead the debrief more effectively and efficiently. If you have the main idea in mind, you can use every interaction with the students to move them towards the main idea.


Take this student’s work. How can the teacher respond to the student in a way that guides them towards the main idea that logarithms give an exponent as an output?

Here are some questions a teacher might ask that align with the main idea:


  • What do you mean by ““gets raised to””?

  • When you say ““the number of the right”” does that mean these equations can only be written like this? What if I wrote 3=Gallas_2_8? Then which number gets raised?

  • Can you explain how the Gallas function tells you what to multiply by?


Notice that the teacher’s first two monitoring questions are aiming at getting the student to make the connection between the function’s output and an exponent, the main idea of the lesson. We’re not focused on the computation in Question #1 of the activity. We’re focusing on the explanation and thinking required.


For the teacher’s third monitoring question, they don’t jump to correct the student, but instead ask the student to explain. It’s likely that the student would say something about how for Gallas_2_8=3 that we multiply 2 by itself 3 times. The teacher can then ask, ““Is there another way we can say or write 2 multiplied by itself 3 times?”” Again, we’re trying to get students to be the ones to generalize that we are talking about exponents.


Knowing the main idea that you want students to understand can help you to focus on the important things, and let the minor things slide. If the lesson is not about graphing and students forget to label their axes, let it go. You have limited interactions with each group, so make sure the conversation is centered on the main idea of the lesson. Being crystal clear in your mind about what this main idea is will help you respond in the moment to groups in a focused way and also allow your debrief to be more efficient. You don’t need to debrief every question and for the questions you do choose to debrief, focus on the reasoning, not the calculations themselves. Spend your debrief time on the most important questions and the main conceptual understanding you want students to take away.

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