We send armed forces recruiters around to the schools, why not send out diplomatic recruiters too? Why not do some interviews on the tv channels to education people.
Most kids and US citizens, for that matter, have no idea about foreign service officer careers unless they grew up in a family of diplomats. I constantly come across kids in university that have no clue about the possibility of a diplomatic career or what people do for the department of state.
Most of the kids I've spoke to about this possibility listen quite intently.