I teach a couple of teenaged boys who were really struggling to make any sound in head voice. I think it’s mostly a coordination thing for them though as they are slowly making progress – they have both gone from making virtually no sound at all to a half reasonable falsetto (still quite weak and breathy though), and I am hoping for even more once we do some proper work on closure We have had to battle a lot of constriction and tongue tension along the way though, so I guess those would be major pitfalls to watch out for? One of them seemed to be trying to actually make the sound with his false vocal folds, so I think it’s just a case of finding the right trigger – using sounds like a mouse squeaking, an owl hooting, or even quoting Monty Python sketches have all worked for me!