I know what you mean. I sometimes offer extra study sessions before class so that I can cater to those students who seem lost and need extra help. As for the students who seem bored, I try to give them more information and challenge them to further motivate themselves so that they aren't so bored.

Perhaps challenge the high achievers by personally contacting them and asking them additional thought-provoking questions, or to provide alterante ways of addressing activities.

Thank you for your initial comment.  I will apply that for my class.  Thanks.