It varies a lot by state and school. I know some schools consider their TAs/RAs as state employees, so they automatically grant in-state and waive tuition. Others say they're ineligible for employee tuition waiver, but they may offer a waiver through the funding package. Still others charge the whole amount straight, but then provide funding to cover it. Those are just what I've encountered; I'm sure there are tons more variations, because anything dealing with money and higher education is convoluted and rarely logical.