Marathon High School (Texas)  Marathon High School is a public high school located in Marathon, Texas (USA). It is part of the Marathon Independent School District located in northeastern Brewster County and classified as a 1A school by the UIL. Typically due to its isolation, Marathon generally has the lowest high school enrollment in the state. Marathon High School serves grades 7-12. In 2015, the school was rated "Met Standard" by the Texas Education Agency. The Marathon Mustangs compete in the following sports -    (Both teams were undefeated). Marathon was also undefeated in 1969 and 1970. Other high schools in Brewster County: