In reply to mc2006:
There is usually snow until June on the high peaks. No glaciers, but still serious and hight mountains. I would have thought it's quite a good place to hold a winter walking / mountaineering course, but obviously not the same as a course in the alps with glaciers. For april, it's probably a good choice though, as conditions are likely to be great.
Not sure about the Cairngorm comparison. They looked very different to me.