This is a fun activity that I like to use. Level Up's work like this:
Everyone is given level I and they work at their own pace. Once the complete level I they must get their answers checked by me.
If they get all the answers correct I stamp their paper and they move to level II and so on.
If they get any answers wrong here's how it works:
1.) the first time you do not tell them what answers they got incorrect, just simply tell them the number of wrong problems... for example: 'you got 2 problems incorrect.'
2.) the second time you either tell them the problem/s that are still incorrect or stamp it and give them the next level.