My 11 year old plays with a western grip, has been since 9 years old. He wanted to hit top spin and so a coach (not in the States) showed him and practiced with him how. I am not a tennis professional so I didn't know what is right and what not. Then in the States two of the coaches he trains with wanted him to change it to semi and worked on it all summer, it didn't take. He tried but they told him when you play a tournament switch back to what you know. He is small for his age so they were worried about injuries from western grip. He trained in Europe all of last summer and I asked two different coaches who worked closely with him about his grip, one said it is perfectly fine and look at the amount of spin he generates. The other one said that my son seems OK with it (hits good and no injury so far), but maybe changing it would be better in the long run to avoid injury. He would have to stop playing tournaments for six months (goes along with why he had a hard time changing to semi in the States), since kids tend to do what they know in order to win, meaning he would play western during matches and that should be avoided.
Anyway, we are done with making any changes with it, I feel like a lot of work was done and no change happened and only makes him question his forehand. He will on occasion have a weird follow through with his forehand, I think because of the western grip. His backhand is his best shot now, maybe because of all that emphasis on changing forehand. We haven’t changed anything for a year now. He hits really good forehands with so much speed and power that after one of these shots he asked me:” Did you see that? Why should I change that?”
Just our little western vs. semi story. I guess we’ll see what happens in the future but it seems majority of the coaches I spoke with think semi is the way to go. I hope this helps you make a right decision for your kid.