I change my scoreboard on a weekly sometimes daily basis. You are not limited to choosing one way to do things, so I am sure you will come up lots of different scoreboard incentives once you begin.
Homework:
I give homework three times per week, I usually pad the assignment to have one or two extra questions, that they don't really have to do - if I want them to win. If I don't think they should win for that day, then I don't assign any extra homework, they are just stuck with their orginal amount.
One the days that we are not playing to reduce the homework assignment, do other things like - bonus points, or quiz vs. game. On a week where are reviewing for a test, I will play all week long to bank time to play a game on Friday. I teach 7th grade, so I am sure 6th graders could handle a week of banking time.
**I also use free time, I let them bank free time for Fridays, and it usually amounts to about four or five minutes, where they can work puzzles, work on HW, talk to their friends. They work really really hard for this, so I don't use it too often, because I don't want the novelty to wear off. This idea doesn't work for everyone, but my students and I love it!