14 CFR § 61.213 - Eligibility requirements.
(1) Be at least 18 years of age;
(2) Be able to read, write, speak, and understand the English language. If the applicant is unable to meet one of these requirements due to medical reasons, then the Administrator may place such operating limitations on that applicant's ground instructor certificate as are necessary;
(i) The learning process;
(ii) Elements of effective teaching;
(iii) Student evaluation and testing;
(iv) Course development;
(v) Lesson planning; and
(vi) Classroom training techniques.
(4) Pass a knowledge test on the aeronautical knowledge areas in—
(1) Holds a ground instructor certificate or flight instructor certificate issued under this part;
(2) Holds a teacher's certificate issued by a State, county, city, or municipality that authorizes the person to teach at an educational level of the 7th grade or higher; or
(3) Is employed as a teacher at an accredited college or university.