pupil vs spring chicken

pupil and spring chicken both are nouns.

Word	Noun	Adjective	Verb	Adverb
pupil	Yes	No	No	No
spring chicken	Yes	No	No	No

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

Other hypernyms of pupil include young person, younker, youth.

pupil (noun)	spring chicken (noun)
the contractile aperture in the center of the iris of the eye; resembles a large black dot	a young chicken having tender meat
a learner who is enrolled in an educational institution	a young person (especially a young man or boy)
a young person attending school (up through senior high school)