During the summer of 1947, Thelma Dewitty was attending graduate school at the University of Washington and writing a mathematics book for children. She had come to Seattle to visit her husband but did not intend to stay if she could not find a job teaching. She had been a teacher in Corpus Christi, Texas, for 14 years.
Her first assignment in Seattle was at Cooper Elementary School in West Seattle. Lester Roblee was her principal and according to Dewitty, teachers were told that a black teacher was to join them and anyone feeling uncomfortable about that could transfer.
During that first year one parent asked that her child be removed from Dewitty’s class. The principal rejected the parent’s request. The teacher said she knew nothing about this until the end of the school year.
She taught at Sandpoint, John Hay, and Laurelhurst Elementary Schools and retired in 1973 from Meany Junior High School. During her tenure at Laurelhurst, she made some profound changes in teachers’ behavior and practices. According to her account, teachers seemed to have assigned seats in the teachers' room at lunch. She chose to sit in a different seat every day and changed a rigid practice. Supplies were distributed to teachers by the secretary but Thelma Dewitty felt that teachers should have an open supply room. Soon supplies became more accessible.
Dewitty said that, because she was a newcomer, she felt some resentment from black pioneers after her appointment as Seattle schools' first black teacher. Some of their daughters, she was told, had to leave the state in order to teach because jobs were not available for black teachers.
In the civic arena, Dewitty was active in the Seattle Branch of the NAACP, serving as its president in the late 1950s. She served on the State Board Against Discrimination and on the Board of Theater Supervisors for Seattle and King County.