From the ATS website:

Overview of Accrediting

Accreditation is about quality assurance for various publics and ongoing improvement for theological schools, especially regarding student learning and formation. It is a voluntary process through which schools mutually assure one another’s educational quality with an eye toward ongoing improvement, based on standards. Through self-review, a school has regular opportunities to reflect intentionally on its distinctive strengths and its areas of desired growth in light of its unique mission and distinct context and in light of the standards.

Self-review then supports the school’s efforts in planning, evaluation, and imagination. Through peer review, an accredited school is endorsed by its peers as one of quality and integrity, which affirms the school’s value to society, as well as its trustworthiness [from Preamble to 2020 Standards of Accreditation].

Commission on Accrediting

The body recognized as the accrediting agency for The Association of Theological Schools in the United States and Canada (“ATS”) is the Commission on Accrediting (“Commission”) of ATS, which is related to but separate from ATS. The current Commission membership includes more than 270 graduate theological schools in the United States and Canada who are Accredited Members.

The purpose of the Commission is “to contribute to the enhancement and improvement of theological education through accreditation . . . [and to] collect data from all members . . . for use in accrediting” (Commission Bylaws, Section 1.2). The Commission is recognized by the United States Secretary of Education and by the Council for Higher Education Accreditation.