Can you please check these sentences for me? Thank you very much in advance.

1)Each group has to interview an American host student for ten minutes and then report about him/her to the whole class (also: present him o her to the whole class).
2) First,build groups of five, six people.
3)I'm teaching German to students between fifteen and eighteen years old (is there a better way of saying it?)
4) I'm teaching them German/how to speak German.
5) The teacher wrote me a reprimand in the class register.
6) It was a man in his fourties, medium-height and well built. He was wearing a baseball cap, a blue-and-white checked shirt and a pair of jeans.
6)Do you know a game called "crew team"?
7) You could repeat most details about your host students (disregarding your grammar mistakes).

1) OK

2) First, build groups of five or six people.

3) I'm teaching German to students who are 15-18 years old.

4) OK

5) The teacher reprimanded me in the class register.

6) It was a man in his forties, who was well built and of medium-height. He was wearing a baseball cap, a blue-and-white checked shirt, and a pair of jeans.

6) Do you know a game called Crew Team?

7) OK

Contrast and compare between another evening at the club and the possibility of evil

Compare and contrast between the possibility of evil and another evening at the club

Contrast and compare between another evening at the club and the possibility of evil 

Sure! Here are the corrected versions of the sentences you provided:

1) Each group has to interview an American host student for ten minutes and then report about him/her to the whole class (also: present him or her to the whole class).
- The sentence is grammatically correct. "Present" is an alternative verb that can be used instead of "report."

2) First, build groups of five or six people.
- The correction here is to change "five, six" to "five or six" for clarity and proper punctuation.

3) I'm teaching German to students between the ages of fifteen and eighteen.
- The phrase "between fifteen and eighteen years old" can be rephrased as "between the ages of fifteen and eighteen" to give it a smoother flow.

4) I'm teaching them the German language.
- The correction is to add "the" before "German" to specify that you are teaching the language itself.

5) The teacher wrote a reprimand for me in the class register.
- The correction includes removing "me" before "a reprimand" to make it grammatically correct.

6) It was a man in his forties, of medium height and well-built. He was wearing a baseball cap, a blue-and-white checked shirt, and a pair of jeans.
- The correction includes changing "fourties" to "forties" for the correct spelling and adding "of" before "medium height" to indicate possession.

7) Do you know a game called "crew team"?
- The sentence is grammatically correct. However, it's worth noting that the term "crew team" usually refers to a rowing team, so you might want to double-check if that's the intended meaning.

8) You could repeat most details about your host students (disregarding your grammar mistakes).
- The sentence is grammatically correct. It suggests that even if there are grammar mistakes, you can still repeat most details about your host students.

I hope this helps! Let me know if you have any more questions.