Ross School was founded by Courtney and Steven J. Ross in 1991. The unique evolution of consciousness "Spiral Curriculum" was designed for the school by the noted cultural historian William Irwin Thompson. The school quickly grew from the initial three students and by 1996 was a full middle school serving girls in grades 5, 6, 7, and 8. The following year a co-ed high school was added, and the first class graduated in 2001. By that time the School was working closely with the Ross Institute to share the Ross Model with other schools and municipalities around the world. In 2002, the Middle School became co-ed and the School began working with its first international partner, Tensta Gymnasium, in Stockholm. In 2005, Ross School received accreditation from the Middle States Association (MSA) and was also chosen to receive the first International Credential ever awarded by MSA.