Dave ... whenever we tweak a system, we try to stay within the original design. So, how about Super Improvers Wall 2.0 means that the kid who gets to the top, gets to pick one other person to join his crew. The two choose a behavior they are both going to work on ... when you see improvement from both of them, they both get a double star! Keep the same number of stars required to move up a color level the same ... but with double stars kids can move up faster. Which is great! Very motivating to get to the top. Both kids on a crew can still earn individual stars ... so theoretically, the bottom kid could catch up. When the bottom kids gets to the top, he can choose another kid to join the two person crew and so on ... thus the Super Improvers Wall is almost infinite ... crews get larger and larger and get to move up faster and faster. At Super Improvers 3.0, they get triple stars whenever all three kids improve on a behavior of their choice (which you have approved).
Tweak this as you wish, but I should get at least a 12 finger woo.