There are several (three that spring to mind are ) - Mirone ski and snowboard, Steves' ski school and Aspen - all do skis and boards, and I know they all have english speaking / english instructors
I stay at the Grand monastery and use Steves Ski School. if you type into Google he has a good website and speaks English. It is situated just across from Grand Monastery within easy walk ( 5mins!) across small nursery slope/sledge run.