classmate
The Italian term for 'classmate' is 'compagno di classe'. It is used in the same context as in English, to denote a fellow student in a class at school. 'Compagno' means mate or comrade and 'di classe' is 'of class'. It is used frequently in academic settings.
My classmate is very intelligent.
This sentence is using 'compagno di classe' to refer to a peer in an academic setting who is intelligent.
Mario, my sister's classmate, is very nice.
In this sentence 'compagno di classe' is used in conjunction with possessive 'mia' to specify that Mario is a classmate of the speaker's sister.
I lent my book to my classmate Luigi.
Here the 'compagno di classe' is the indirect object indicating that Luigi, the speaker's classmate, was given a loan of a book.