I have coached High School for several years. I also coached my youngest who is 14 for three years in AAU starting out at 10U. I won two state titles and finished in the top 10 D-1 twice at 12U and 13U Nationally. We went 38-2 one year 35-6 one year. And we never threw one stinking curve ball. Four seam fastball, 2 seam fastball, change up and changed speeds on our fastballs. I faced team after team at all these age levels even 10U and curve after curve ball. I refused to let kids this age take the risk of arm injury because I dont feel that they are mature enough physically to handle the strain on throwing a cb even when properly taught. Its not worth the risk period. I also wanted them to rely on learning how to pitch. Meaning change speeds and hit location and setting up batters etc. Not to rely on a gimmick pitch because at that level thats all it is. Hey this is just my opinion please dont take offense. Its just my opinion.