7th Grade Whole Class Reward/Incentive Program. Suggestions needed.

I'm looking to begin a whole class reward system for my 7th grade ELA classes. I have the basic idea of filling up mason jars with marbles. Every positive action = another marble in the jar. When a class fills the jar, they get a treat (candy/prize etc.)

I would appreciate any constructive criticism on this idea.

I would also like some suggestions for reasons to add marbles to the jar. Some ideas I had are: -Every student completes last night's HW -Every student passes quiz -Marble for every Accelerated Reader Quiz passed -Marble for solid class participation that day -Marble for kind/supportive actions

What else you got?