In 2008, ISM earned joint accreditation by the Western Association of Schools and Colleges and the Council of International Schools.

ISM joined 382 schools with the prestigious CIS accreditation, and is one of just 10 such schools in the United States and the first public charter school to earn this recognition. The combined WASC/CIS accreditation recognizes that the school has “achieved high standards of professional performance in international education and has a commitment to its continuing improvement.”

Both CIS and WASC renewed ISM's accreditation for five years through 2023 following a comprehensive visit by both organizations along with International Baccalaureate Primary Years Programme and Middle Years Programme teams in Spring 2018.

ISM became the first public school in the United States to be granted candidate status for joint accreditation by WASC and CIS in February 2005. Subsequently, the school has engaged in the ongoing self-analysis and self-improvement that serves as the greatest benefit of the accreditation process. This, coupled with the valuable input of WASC-CIS visiting teams and subsequent requirements and reports, has led to extensive refinements and improvements to the ISM educational program as well as the school’s operations.

Overall, the accreditation process focuses the ISM community's attention on all critical aspects of school effectiveness, and the awarding of CIS and WASC  joint accreditation provides the strongest possible stamp of excellence for an international school.