I think this question is different for pitchers and position players. As a pitcher, U12 is the year they go from 35 to 40 and small ball to big ball. The first year can be difficult. I think a pitcher should pitch the second year at U12 and dominate (if they are that good). I think that's a confidence builder. Then jumping from U 12 to U14 and even U16 will be easier. No need to play 2 years at U14. I know my younger daughter was a good pitcher at U12 the first year but had a great year this year at 2nd year U12. She grew 4 inches this year. Her speed jumped 4-5 mph during the year. And when we played in this fall at U14, she was ready. I'm glad we waited and played 2 years at 12 U.