class period vs session

class period and session both are nouns.

Word	Noun	Adjective	Verb	Adverb
class period	Yes	No	No	No
session	Yes	No	No	No

As nouns, session is a hypernym of class period; that is, session is a word with a broader meaning than class period:

class period (noun)	session (noun)
a regularly scheduled session as part of a course of study	a meeting devoted to a particular activity
	a meeting for execution of a group's functions
	a meeting of spiritualists
	the time during which a school holds classes