What is the difference between 学生 and 生徒 ?
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(○○high school)の生徒 (student) / ○○中学(○○ junior high school)の生徒 (student) 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.
(1) わたしは ABC大学の 学生です。
→ I am a student at the university of ABC.
(2)クラスに 生徒が ２０人 います。
→ There are 20 students in the classroom.