In our local kids rec league, there are rules differences in 3/4, 5/6, 7/8 and HS levels. Of course we give each ref a copy of the rules and have meetings to go over them before the season starts. However, it still can get confusing, especially if you work different levels on the same day.
So.....here's what I do. I make up a rules "matrix". It's a grid that shows the grade level on the top, the situation on the left side (defense allowed, timeouts, quarter timing, etc.) and then the rule for that level where they intersect. It's just a standard Excel file. The refs carry it in their bags with their rules and just check it before the game. Sometimes, they put it out on the table. It's easy to make up and it really helps.
Obviously, I could have put a "Matrix" pic here, but that would have been too easy.
