The big difference is between input and output tasks for pupils. Input tasks means that the task (eg. a homework) just has to be done like learning vocabulary or reading a book. Either you do them or not, there is no middleground. Output tasks on the other hand are about the result and even if pupils do the task, they can still fail. An example would be to write a poem that rhymes, where some can be subjectively better than others.

Research shows that pupils are much better with input tasks with an objective result than interpretable output tasks. If you let them only do input tasks, you will get better results (I am referring to Ronald Fryers work), which should also count for homework.

Maybe giving them a candy or a Euro for having done the homework works and if I was a teacher, I would make them use a camera while doing the homework as proof of not cheating.

Also: Give the good pupils a day off. I never understood why you don't get a day off as a reward when having an (objectively measurable) A grade plus also one day off for two B's.

I was notoriously lazy and stubborn because I didn't see the sense in getting up in the middle of the night just to go to a place to do things that I don't want to do. But with that incentive, I would have done anything to get away from it as often as possible.