i used to take horses for professional schooling, and it's worth it if you are prepared to be involved and learn from it as well. i have a few horror stories of people with "difficult" horses who they sent to me, and because the problems were created by the rider, as soon as they left the problems came back. also people who had young horses, and expected them to go to me for 6 weeks and come back schoolmasters.
from your point of view, i wouldn't send my horse anywhere where they aren't happy for you to come and visit unannounced, watch their people riding your horse, or don't encourage you to have lessons with the person that's doing the schooling. if you're more the dorset end of hampshire, i can ask at the yard at the weekend - we aren't taking horses for schooling since i stopped working there full time, but the yard owner is bound to know someone. we do livery, though, so if you do get one, i can give you the number if you'd like. it is a busy yard with children, but plenty of adults as well and ideal for novice owners. i've been there for 15 years and wouldn't keep mine anywhere else.