1 - Transaction motive

2 - Precautionary motive

3 - Speculative motive

my motive in school is to get good grades

No. Motive is wether or not you had something to gain. Intent is if you did something for sure but what was the reason behind it.

A by-motive is a hidden motive.

An ulterior motive is a motive that they have beyond the main motive. They often do not show that they have this motive and it is often not good. The ulterior motive is almost always has it for their own good only.