"To understand the lesson" means to comprehend and grasp the knowledge being taught or explained. It means you can absorb and make sense of the information effectively. Full definition
It provides real time information on how well students understand a lesson and gives you a window into their thought process as they explore new concepts. (classtechtips.com)
In large measure, this reflects the failure of policymakers and the public at large to understand the lessons of opportunity costs. (johnquiggin.com)
If students didn't understand the lesson from the day, not understanding 20 problems may make them feel that math is inaccessible. (edutopia.org)