If you don't they will forget it all. Bring the less knowledgeable students up to the level of the more knowledgeable ones before proceeding further. Encourage peer teaching at this early stage. Allow those students who are only interested in passing the course a way to do so which is fair to you, to them, and to the institution. Be enthusiastic about the course material.
Enthusiasm is contagious.
You may initiate a discussion by setting a problem, by asking an open- ended question, or by beginning with a controversy. Invite them to speculate. Allow them to play with ideas. Learning depends on the process of discovery - Ruth C.Cohn To increase participation, talk less and listen more. Encourage the students to talk directly to one another instead of going through you each time.