To see how one classroom is doing against the others, use the Classrooms view in Insights.
Getting there
Click Insights in the sidebar. You need to be an organisation admin to see it.
Click Classrooms, then click a classroom in the table to open its detail.
For the day-to-day view of a single class, the classroom's own Insights tab is usually more useful.
Everything on these pages respects the date range in the top right, which defaults to the last three months. Change it to compare a term against the one before.