Insights on a lesson assignment tell you how the class handled it, and which misconceptions are worth going back over.
Opening them
Open the classroom, go to Assignments, click the assignment and then the lesson. The activity page has three tabs: Students, Blocks and Insights.
The Insights tab surfaces the themes across the class, rather than making you read thirty scripts to find them.
The Blocks tab is the manual version: pick a question and see how everyone answered it.

