Middlesex School is a coeducational, non-sectarian, day and boarding independent secondary school for grades 9-12 located in Concord, Massachusetts. The school is a member of the Independent School League and is one of five schools collectively known as St. Grottlesex.

Tuition + boarding $69,280. Cost of books totals an estimated $1,000 per year. International students must purchase health insurance for approximately $3,000 per year.