What is the difference between 学生 and 生徒 ?

What is the difference between 学生 and 生徒 ?

学生がくせい are who studies (at some institution).
生徒せいと 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 ○○高校こうこう(○○high school)の生徒 (student)   / ○○中学ちゅうがく(○○ junior high school)の生徒 (student)  or
just 高校生こうこうせい、中学生ちゅうがくせい in general.

学生 for high school or middle school students is acceptable, but not so common. 

・Sample sentences 

(1) わたしは　ABC大学だいがくの　学生がくせいです。

  → I am a student at the university of  ABC.

(2)クラスに　生徒せいとが　２０人にん　います。

  → There are 20 students in the classroom.