If you are early

If you are early to school and the classroom is still locked then go to the administrator in the office and ask for the key. Say something like:

"oh, good morning, um, could I please have the key for L11?

The administrator might say comments to you like:

Admin: oh, it's cold this morning isn't it?

You: oh, yes, it is, I need to try to keep warm.

Admin: here it is.

You: oh, thanks very much, I'll return it soon.

Admin: thanks, have a nice day.

You: oh, thanks, you too.

If you are waiting outside for the administrator to open the main door then you can knock on the window. The administrator will then open the door for you. In this situation you should say:

You: oh, thanks very much

or

You: oh, thanks, I really appreciate you opening the door because it's very cold (ha ha).