My son is a low 3/4 guy. No one taught him to throw that way. Just his natural slot. He has a lot of movement on his fastball and throws it pretty hard. He does not have a 12-6 curve, but has a good change up as well as a cut fastball/slider that breaks down and away from RHB's (RHP). His fastball tails in on RHB's.
His pitching coach is a AA minor league pitching coach and every year he tells us, more than once "Don't let anyone change his arm slot". He has been very effective up to this point.
He is a 15 year old freshman and has never had any arm problems. I have always been leery about changing someone's arm slot. I think when you do that, you are not throwing naturally and could be more prone to injury. JMO.