Personally, I don’t remember the specific phrase “parallel terms” from my school days, but I’m guessing that it has to do with verb agreement. That is, an INCORRECT way to write the sentence would be, for instance:

“…it is as important to take thorough notes as reading every assignment.”

This would not be parallel, since the two verbs–“take” and “reading”–are not in the same form. They would either have to be “taking” and “reading”, or “take” and “read”, as they are in your original sentence.

But if I’m interpreting the question incorrectly, then someone else please help to clarify or correct my information! 🙂