Student or Learner
What is the meaning of 'a few of' in this phrase 'all but a few of 50,000 students...'?
Another way of putting it would be "the vast majority" but there would still be a subtle difference between the two phrases.
I'm not sure that it can be explained any simpler than that.
By the way, it should probably read "all but a few of the 50,000 students...".
NB I am a native British English speaker, not a teacher.