学生 are who studies (at some institution). 生徒 are who are taught (from some teacher). College(or higher) students are normally called 学生。 High school and middle school students are normally called ○○高校 /中学の生徒 or just 高校生、中学生 in general. 学生for high school or middle school students is acceptable, but not so common. Tutees can be called 生徒, as well.

学生 and 生徒 is equivalent to students and pupils in English. 生徒 may also be interpreted as apprentice.

学生maybe just in the school,but 生徒don't need to,they learn from their mastor