I told my soldiers that they had to do a minimum of 10hrs of Correspondence courses
I commend you for setting the standard and helping them progress... however be careful on how you word the counselings. You cant MAKE them do these things, and many CoC's will let you know that off the bat. These things aren't madatory (even if I or you would like them to be) so you technically can't punish them for not doing something considered "elective".
However what you can do when they DONT do these things is counsel them on not meeting standards, and let them know that when it comes time for advancement they will not be recommended. This is the best motivator in my opinion.
I would not recommend any Soldeir for addvancement/promotion who cannont follow these simple instructions of bettering themselves. If you push that angle in the cousneling session (and on paper) and anyone above you (PSG or 1SG) wants to knwo why you dont recommend their advancement/promotion then you have it on paper that they cant do the most simple of things, i.e. follow proper direction.