In your case, as a graduate student with a teaching role (a "scholar") you become a tax resident, who would be eligible to file using TurboTax on January 1st of the third calendar year that you are in the United States if your Visa is a J-1 Q-1, or Q-2.
The IRS addresses this topic a number of different places, so it does get rather confusing. I found this reference here: Foreign Student Tax Liability
See this IRS excerpt from that link : Foreign scholars, teachers, researchers, trainees, physicians, au pairs, summer camp workers, and other non-students who enter the United States on J-1, Q-1 or Q-2 visas usually become RESIDENT ALIENS on January 1st of their third calendar year in the United States. Foreign students who enter the United States on F-1, J-1, M-1, Q-1 or Q-2 visas usually become resident aliens on January 1st of their sixth calendar year in the United States.
If this doesn't answer your question, please let me know and I'll keep looking for more information!
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