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 CIS accreditation, was one of just 10 such schools in the United States, and was the first public charter school to earn this recognition.  The combined WASC/CIS accreditation recognized that the school had “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 Program and Middle Years Program teams in Spring 2018.  In 2023, ISM chose to continue with the WASC accreditation process for future years.

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 ongoing self-analysis and self-improvement, which is the greatest benefit of the accreditation process.  This, coupled with the valuable input from WASC-CIS visiting teams and subsequent requirements and reports, has led to extensive refinements and improvements to the ISM educational program and 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 IB and WASC joint accreditation provides the strongest possible stamp of excellence for an international school.