I've been teaching the Salmonid in the Classroom program for 16 years now and like Schenley said it's an educational program to teach the kids about the importance of water quality, conservation, it being a renewable resource, and of course the life cycle of the salmon. All the schools get their eggs from the closest hatchery because they need to be returned to that system. You can't transplant them where you like. Sometimes the returns of coho are so poor or they lose the eggs through disease that they can ill afford to give them to the schools and must take extra precaution to make sure as many survive as possible. They never usually have a problem with chum numbers and like Biffchan said, their survival rate is much better because they swim directly to the ocean as fry. They never have to worry about low or warm water conditions.
Talk to any biologist in the field and they'll tell you that the number of eggs that all the schools are given in total (approx. 50 to each school) is just a drop in the bucket when it comes to fish enhancement and not even noticeable. Hatcheries that literally raise millions have difficulty improving overall river numbers alot of the time. Just take a look at the number of rivers in the province that have some form of enhancement program but still don't allow sports fishing on their systems yet.
BTW, this is a fed. program so forget about EVER seeing steelhead in classroom situations because all enhancement of steelhead is still under provincial jurisdiction. They still have heated debates about having steelhead enhancement in any river where wild ones still exist. ie. Thompson R.