See this pamphlet to determine if you were considered a PA resident for tax purposes:
http://www.revenue.pa.gov/FormsandPublications/FormsforIndividuals/Documents/Personal%20Income%20Tax...
If you were only in PA for a specific period of time (such as graduate school sessions) then it appears you would be a non-resident for income tax purposes. If your living in PA becomes indefinite at any time, then you became a resident of PA (such as taking a job where the end date is indefinite).
If you are a dependent of your parents, you would remain a resident of the state of your parents with temporary absence from home for schooling.