To qualify for lower in-state tuition rates at public universities in most states, you must be able to demonstrate that you were a resident of that state for a certain amount of time before you enrolled. Tennessee is different. According to the College Board, Tennessee is the only state, as of 2011, that doesn't have such a "durational requirement" to qualify for in-state tuition rates.
Under the residency rules used by all of Tennessee's public universities and community colleges, you need to demonstrate only that your "domicile" is in Tennessee to qualify for in-state tuition. Your domicile is essentially your permanent address. As the residency rules put it, it's where you "intend to remain" and where you "expect to return" if you leave the state temporarily. If you're younger than 18 or are still being supported by your parents or a legal guardian, then your parents' or guardian's domicile is also your domicile. If your parents are divorced, you can use the domicile of either parent, regardless of who has custody.
It's up to you to prove that your domicile is in Tennessee. The residency rules do not describe what constitutes sufficient proof. However, in response to inquiries from the College Board, officials at the University of Tennessee gave examples of acceptable documentation. They include a Tennessee driver's license, vehicle registration or voter registration; tax returns showing a Tennessee address; proof of employment in Tennessee; or military documents that show a permanent address in Tennessee.
The residency rules give each school the responsibility for determining whether its students qualify for in-state tuition. Each school has a "classification officer" whose job is to make such determinations. The rules instruct classification officers to consider "any and all evidence" of domicile, but to accept no particular item as conclusive proof. In other words, no one single document proves beyond a doubt that your domicile is in Tennessee. The officer will classify you based on the totality of the evidence. If you disagree with the classification, you can appeal.
If you're already enrolled at a school and paying in-state tuition rates, you can continue doing so if your parents or guardian move their domicile out of the state. You must remain continuously enrolled to maintain in-state status, though. If your school determines that your legal guardianship was established solely for the purpose of establishing domicile -- for example, if your parents sent you to live with an uncle in Tennessee so you could get in-state rates -- then it will classify you as an out-of-state student. Under state law, illegal immigrants cannot claim a domicile in Tennessee to get in-state tuition rates, regardless of how long they have lived in the state.