What should I do if a lesson is not working, perhaps because the students do not understand the material?
I would imagine that every teacher has tried a lesson that just didn't work for one reason or another! Here are some ideas:
Be flexible. Always be willing to change or even abandon your lesson plan.
Stop the lesson and go over the material students do not understand. Don't worry if you are not able to get through as much as you had planned - the important thing is that the students learn. Change test dates or due dates if you have to.
Very important: be ...
Even the best lesson plans are sometimes ineffective for several reasons. Here are some ideas on what to do if a lesson is not working when students are not understanding the lesson content.