You might also consider social philosophy and critical whiteness studies. The norms of critical whiteness–a socially-constructed system that is normalized within a system of privilege that is taken for granted by those who benefit from it (Barbara Applebaum) could be unintentionally reproduced in the Montessori system. I think Critical Race Theory in education could also provide an effective lens, in that, systems of education have been developed with racism and privilege “baked in.” You have some good suggestions from your fellow students that might be appropriate for your literature review.