Originally Posted by
night mission
As mentioned in an earlier post, only 3rd class required in the USA.
That was wrong then and it's still wrong now. NO medical is required to instruct in USA unless the instructor is required act as pilot in command and needs a medical certification of some sort to be pilot in command. Even then basic med will often be sufficient.
Instructing in gliders requires no medical certification even if the instructor is pilot in command. Instructing in SEL requires no medical if the "student" is current and qualified to be PIC. So, no medical needed for flight reviews, tail wheel instruction, tow pilot training, jump pilot training, aerobatic instruction, commercial instruction in TAA, etc as long as the "student" has privilege to act as PIC and is qualified to act as PIC.