I am currently paying child support for my 18 year old son. He started going to school in September but recently dropped out. He is working 2 days a week.
If he stops going to school, am I still responsible to pay child support?
I was told that if the child stops going to school, he must be working full time in order for me to stop paying. Is that true?

This depends a lot on your support agreement. The agreement usually is written to cover this situations so you need to reviewe it. If the agreement is mum on the issue then you need to default to your state laws.

Yes, it can depend on factos, the state you live in, and what the exact wording of your child support agreement states.