Fertile hatchery fish have, on average, around only 10% of the survival and breeding success that wild fish do.
Hybrids that arise from hatchery fish mated with wild fish have only 50% of the survival and breeding success.
Therefore, continuing to stock fertile hatchery strain fish tends to reduce the population of trout which are able to breed by themselves (this is the reason for the National Trout and Grayling strategy moving stocking over to sterile hatchery fish by 2015).
The shorter answer would also be that the classroom trout will be subject to the NT&G strategy by 2015.