We love this ski school as the classes are small (6 for children and 8 for adults) and the instructors are very good at English. If you want to make sure that your child is happy at ski school use Eskimos. The classes are from 9.30am-12.30pm so they avoid the lift queues as Swiss Ski School starts at 10am and you get to have lunch with your children afterwards.
The only problems that we have encountered is when there are not enough people to run a certain class which has meant that you (or your child) has to ski down a class or hire a private instructor. Our 11 year old has got to the top children's class and come out of the top of it so we have changed resorts. But we loved the Eskimos and our 3 children ski well and have adored all their Eskimo instructors and classes!