Without knowing the spcifics of your situation. Usually, a "C" school is done in conjunction with a PCS move or as an incentive for a reenlistment. A Command and Detailer would not normally give someone a "C" school unless it was a required NEC billet that needed to be filled. Check your PCEDVR for your required billets. Also check our MILPERSMAN 1306-600 series for Service school requirements.
Second question is: was there a deal made between the Command and Detailer about his transfer? because i'm pretty sure if the Command knew his intention was to leave, he would not have gotten the school. What program was he trying to use to transfer, Split-Tour?
So, bottom line is the Commanding Officer has the final say.