Hello,
As Dresq said, each player is only allowed to help other players ten times each week, if that player is not also on the same level as you, yourself are on.

For example, if all players are on level 20, then you may complete any number of these team exams together. Likewise, if all players are on level 23, there is no penalty and nothing is tracked. However, if one player is on level 25, and one player is on level 1, then the player on level 25 only has 10 levels they can help the player on level 1.
If, however, the lower player catches up to the higher player, they could then resume player together with no penalty. I.e., if players were on levels 15 and 18, the player on 15 would catch up to 18, and the player on 18 would use 3 of their weekly 10 chances, the players would synchronize, and then no more of the weekly 10 chances would be used. The players would then be in sync, and the players could proceed together as normal.
Hope that helps!