Original Source: Harvard Admission website.
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Frequently Asked Questions: Admissions
Teachers who know the applicant well and who have taught him or her in academic subjects (preferably in the final two years of secondary school) most often provide us with the most valuable testimony.
While we can make careful evaluations with required recommendations, we are happy to read helpful letters from people directly familiar with applicants’ lives outside the classroom. Such letters are not necessary, however, and it is generally advisable to submit no more than two or three.