How to say these school related things in Japanese?

Question:

So school related things, how would I say:

I have homework.
Shukudai ga aru.

Do you have any homework?
Shukudai ga aru ka?

I'm in Highschool
Watashi wa koutougakkou de desu.

My classmate is weird
Watashi no doukyuusei okashii/ha desu.

My teacher teaches bad.
Watashi no sensei dame oshieru.

If I'm saying these wrong please correct me. Any help is apreciated and helpful. If there is a more natural japanese way of saying this, please help. Any explantation to anything you post is most helpful too. Thank you in advance for choosing your answer, if chosen to answer. Much appreciated!

Answer:

I have homework.
Shukudai ga aru.
-Shukudai ga arimasu (formal)

Do you have any homework?
Shukudai ga aru ka?
-Shukudai wa arimasuka?

I'm in Highschool
Watashi wa koutougakkou de desu.
-Watashi wa koukou ni kayotte imasu.

My classmate is weird
Watashi no doukyuusei okashii/ha desu.
-Watashi no doukyuusei wa okashii desu.

My teacher teaches bad.
Watashi no sensei dame oshieru.
-Watashi no sensei wa oshie kata ga warui.