I actually administered Tanner staging tests to teens of various ages (to be precise at 10yrs, 14yrs, and 18-20yrs). Tl;dr: Tanner staging can be done through self-reports as well.I was participating in a student research group and we were studying how puberty affects a certain neurological function (nothing sexual, just a regular brain function that I'm too lazy to explain right now). And we were using EEG measures, so there was no nudity involved.So that way it worked is that we gave our subjects a questionnaire in which they self-reported their development (e.g. hair growth, genital growth, etc.) and that was good enough to get an estimate on their Tanner staging.I guess that Tanner staging on medical exam forms work about the same way, except that the doctor gets a visual on puberty development and just crosses the box that fits best.