My 14YO DD starting using the weighted balls during practice and a little as part of her warmup routine last year. As part of practice we would use all three balls of the set starting with the lightest for 8-10 reps then moving up with the same reps for each of the other two. After using the balls, she showed increased speed and control. She only uses them with part motion - rocking it up to just past 9 (3?) and then throwing. We concetrate on timing and mechanics while using these, thern immediately afterwards "let 'er fly". It seemed to help last year anyway. Haven't started using them yet this year.