What if assistant teaching is being used as a verb? Hyphenated or not? As in:

Question

I have been assisant teaching with my grandmother for four years.

Answer 1

In that case, "assistant-teaching" would be hyphenated, yes.

http://grammar.ccc.commnet.edu/grammar/marks/hyphen.htm
Here is an excellent section on the uses of hyphens. Scroll down and note the part called Hyphens have other uses, especially "a."