14 CFR 147.19: Instructor requirements.

Each certificated aviation maintenance technician school must:

(a) Provide qualified instructors to teach in a manner that ensures positive educational outcomes are achieved;

(b) Ensure instructors either—

(1) Hold a mechanic certificate with one or more appropriate ratings; or

(2) If they do not hold a mechanic certificate, are otherwise specifically qualified to teach their assigned content; and

(c) Ensure the student-to-instructor ratio does not exceed 25:1 for any shop class.