Dear Ms. Domingue,
Thank you for posting on History Hub!
The National Archives and Records Administration has many different types of records related to Bureau of Indian Affairs schools. The records are held at various NARA facilities across the nation.
For a list of schools, please visit https://www.archives.gov/research/native-americans/bia-guide/schools. There are many schools listed for Oklahoma. Next to each school name is information on where to find records for that school.
For more information on administrative records including registers, school applications, and medical records, please visit https://www.archives.gov/research/native-americans/schools/school-records-more.
For student case files from non-reservation boarding schools, please visit https://www.archives.gov/research/native-americans/schools/school-records-more.
We hope this information proves useful to your research!