Maybe you should stop treating them like slaves who just need to sit there and download whatever you tell them?
How about asking them what they want to learn?
They probably won't get to live to 50 considering the destruction we have done to the climate because of our greed and consumerism. Cut them some slack.
Try this https://www.amazon.com/Why-We-What-Understanding-Self-Motivation/dp/0140255265
Did you ever ask them if they wanted to learn what you were teaching them?
Did you ever ask them to give you input on what they wanted to learn?
Intrinsic motivation is more powerful than extrinsic motivation in many cases. People aren't puppets.