The principal function of ISACS is the accreditation of its member schools, which, as independent not-for-profit schools, have voluntarily chosen to guide their progress toward an ideal of educational excellence by measuring against the highest possible standards. In providing and developing standards of excellence, ISACS in no way limits, but strives to preserve, the freedom of each individual school to practice its own theory and philosophy of education.

Independent schools differ from other non-public schools in that they generally have the following characteristics:

They are governed by a board of trustees.

They are fiscally independent. (Roman Catholic and Anglican "order" schools such as Benedictine, Jesuit, Sacred Heart, etc. as well as certain other Christian and Jewish day schools, are considered to be fiscally independent so long as they control their own finances).

They have a stated policy of nondiscrimination in admissions and employment.

They are recognized by the Internal Revenue Service as non-profit 501(c)(3) organizations.

They are approved through a recognized accreditation process, such as that provided by the six regional accrediting bodies and certain independent school associations.

While ISACS member schools may, and do, vary significantly in their purpose, program, and style, they are all subject to certain means of accountability including the following:

They must satisfy their constituencies concerning the quality of their educational program and services since enrollment of students and voluntary financial support depend upon such satisfaction.

They must meet the published standards of ISACS (see ISACS Standards for Membership, Appendix A) which include standards on corporate status, nondiscriminatory enrollment, and hiring policies and procedures, as well as some specific requirements concerning the school's structure, governance, administration, faculty and staff, and overall program.

They must demonstrate their commitment to quality and growth through participation in the seven-year cycle of the accreditation process as established by the board of trustees.