4seamer. I agree with that. As I stated earlier, I personally don't have a problem with throwing breaking balls at that age as long as you are doing it right and as long as you don't rely on it without continuing to develop your FB and CU.
Like I said, my son relied more on the FB/breaking ball combo at that time due to his FB velo.
By the way, our HS coaches were very concerned about pitchers arm health. Starts were generally 1x per week. All pitchers had pitch counts. Rest between starts was a big deal. I really didn't see too many guys overthrown. Realize that in HS, you generally only play 3 games a week. Unless you have rainouts to make up and you have to squeeze a bunch of games in a short period of time. In that case, you will need more pitchers.