Depends on the phase...
For API, my class started with 24, graduated like 26 (rolled a few out of the class, rolled a few into the class). The class before mine had twice that.
All depends on what the pipelines are doing.
Also, you don't stay with the same people the whole time. You'll more or less stay about with the people that track the same as you do.
Due to injuries, academics, personal issues, and other reasons, the number of studs in a class for a particular phase can and will fluctuate due to people dropping from the class and others being picked up midstream.