CATCH UP ON

If you have work you need to catch up on, you're behind. If you want to catch up on the news, it means you're not as informed as you want to be. If you need to catch up with a friend, you haven't been in touch as often as you meant to be. So I would agree with your teacher that it means that something didn't happen that was supposed to have happened, whether it was your work, your level of being informed, or keeping in touch with your friend.

However, I disagree with your teacher over the use of the word "never."

Because can always start a setence as a dependent clause, even in formal writing. Because she had no where else to go, Rose was forced to seek refuge with her domineering father. Because my boss is a nice guy, he's giving us Friday afternoon off.

In formal writing, because should not start a "sentence" like "Because he was happy to be home." That's not a complete sentence at all. If you are asked a question, you shouldn't reply (on a test) with a construction like that.

However, in informal speech, it's used like that all the time.

Hi Matthew.

Glad you like the name. Of course, after I chose it, I realize how little I know about the actual workings of grammar. I should have chosen something like "Writer Geek." But too late now!

I gave you examples of "Catch up on" and that is indeed different from "catch up to." That can mean both physically - say we are walking and you stop to tie your shoe lace and then have to hurry to catch up to me" or abstractly - if you miss a lot of school, you may have to read a lot to catch up to your classmates.

And yes, you can certainly say "Because I woke up late" in casual conversation. However, if you teacher asks you, you should say "I'm late to class because I..." and not start right in with "Because..."