In the Marine Corps your promotion to E4 and E5 is based on your composite score and your MOS's cutting score.  Your composite score is based on your pro's and con's and your PFT score and rifle score.  They also give you points for how long you've been in and how long you've been at the rank you are.  To get promoted to E6 you have to have been an E5 for at least 2 years before you are eligible to pick up (unless it is a field (combat) promotion)then it is up to recommendations from your SNCO's and up.  They don't have NCO school they have CPL's Course and SGT's Course some MOS's require you to go some recommend you go and some could care less if you go or not.