der Klassenraum
classroom
A room in a school building where lessons for a school class take place.
Die Schüler betraten nach der Pause den Klassenraum.
The students entered the classroom after the break.

classroom
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classroom
A room in a school building where lessons for a school class take place.
Die Schüler betraten nach der Pause den Klassenraum.
The students entered the classroom after the break.

The word is a clear compound of 'Klasse' (class, in the sense of a school class) and 'Raum' (room). The 'n' in between is a linking n that connects the two words.
Der Klassenraum der 5b ist im ersten Stock.
Classroom 5b is on the first floor.
With the preposition 'in', pay attention to the correct case: 'in den Klassenraum' (into the classroom, accusative) describes movement, while 'im Klassenraum' (in the classroom, dative) describes the location.
Die Lehrerin kommt in den Klassenraum.
The teacher comes into the classroom.
Typical verbs in connection with 'Klassenraum' (classroom) are 'betreten' (to enter), 'verlassen' (to leave), 'aufräumen' (to tidy up), or 'schmücken' (to decorate).
Nach dem Unterricht müssen die Schüler den Klassenraum aufräumen.
After class, the students have to tidy up the classroom.
class
In everyday school life, 'die Klasse' and 'der Klassenraum' can both have to do with the place where lessons happen. 'der Klassenraum' clearly means the room where teaching takes place. 'die Klasse' usually means the group of students, but it can sometimes also be used as a short form for the room. That is exactly why confusion can happen. If you definitely mean the room, 'der Klassenraum' is clearer. If you mean the group of students, 'die Klasse' fits.

Der Klassenraum wird vor dem Elternabend noch sauber gemacht.
The classroom is cleaned before the parents' evening.
Nach der Pause wartet die Lehrerin, bis die Klasse wieder ruhig ist.
After the break, the teacher waits until the class is quiet again.