Middlesex School | 3,329 followers on LinkedIn. An independent, co-educational boarding school in Concord, MA for grades 9-12. | Welcome to Middlesex School! We are an independent secondary school for grades 9-12, offering students the opportunity to live on campus and participate fully in the life of a busy, residential school environment or to attend the school as day students. Our curriculum is rich and demanding, and our extracurricular programs highlight our belief in the development of all aspects of a young person's life.