How to Strengthen Your Kid's Writing Grip (a New Purpose for Pennies)! by Margaret Steck
When my daughter started kindergarten, her teacher told me that we needed to work on improving her writing grip. One of the exercises he showed us that has helped is to have her pick up pennies one by one in a smooth, controlled fashion and place them into the palm of the same hand. The key is to keep those coins in the palm of that hand while she continues to pick up pennies, moving them with her fingers backwards into her palm.
So far, it's worked great! And I even let her keep the pennies as her prize, so she really enjoys doing it.