Shortly after graduating from Miami in 1928, Ewbank took his first coaching job at Van Wert High School in Van Wert, Ohio, overseeing the football, basketball and baseball teams. He remained there until 1930, when he moved back to Oxford and took a position coaching football and basketball at McGuffey High School, a private institution run by Miami University. He also taught physical education at Miami. Ewbank took a break from coaching in 1932 to pursue a master's degree at Columbia University in New York City and filled in as Miami's basketball coach in 1939 after the previous coach left for another job, but otherwise held his coaching positions at McGuffey until 1943. Under his tutelage, the school's Green Devils football team had a win–loss record of 71–21 in thirteen seasons. This included a streak of three undefeated seasons between 1936 and 1939 and one season – 1936 – where the team did not allow any scoring by opponents.