I didn’t read the responses, I apologize if I repeated what someone else said.
I don’t know if this is possible or practical but maybe you can approach your sons Rebbe or teacher (or a former teacher that looked out for him and you had some contact with- that may be even better) and ask to institute something like that for Elul or as a project for the year without involving your son directly. (A teacher would know right away but it won’t be at the school level and maybe he can avoid the “stigma” for future years)
Now hows that for a run on?
Hatzlacha