schoolboy vs pupil

schoolboy and pupil both are nouns.

Word	Noun	Adjective	Verb	Adverb
schoolboy	Yes	No	No	No
pupil	Yes	No	No	No

As nouns, pupil is a hypernym of schoolboy; that is, pupil is a word with a broader meaning than schoolboy:

Other hypernyms of schoolboy include boy, male child, adult male, man, school-age child, schoolchild.

schoolboy (noun)	pupil (noun)
a boy attending school	the contractile aperture in the center of the iris of the eye; resembles a large black dot
	a learner who is enrolled in an educational institution
	a young person attending school (up through senior high school)