The school opened in 1955 as Somerford Secondary Modern School and became The Grange in 1969 when it went comprehensive, at the time Christchurch being in Hampshire until 1974 when it became part of Dorset, the school becoming part of Dorset LEA.
The school converted to academy status on 1 February 2015 and is now part of the Twynham Learning multi-academy trust. In the summer of 2021 The Grange School underwent a significant restructure formalising its relationship with Twynham School. The Twynham Learning offices relocated to The Grange School campus along with the successful BDP SCITT and the professional development hub, Two Rivers Institute. In December 2021 The Grange School was judged to be "good" in all areas by Ofsted.