This might help you out.
Type of MOS : PMOS (Primary MOS)
Rank Range: MGySgt to SSgt
Job Description: The infantry unit leader assists commanders and operations officers in the training, deployment and tactical employment of rifle, weapons, LAR, and antitank platoons/companies and infantry, and LAR battalions, are proficient in all the infantry weapons systems. They supervise and coordinate the preparation of personnel, weapons and equipment for movement and combat, the establishment and operation of unit command posts, the fire and movement between tactical units, the fire of supporting arms, and the unit resupply and casualty evacuation effort. As a platoon sergeant or section leader in the rifle, scout sniper, weapons, heavy machinegun, LAR, and anti-armor platoons, he advises the platoon commander on all issues of discipline, morale and welfare.
Job Requirements: Complete the Infantry Unit Leader Course at SDI, Camp Pendleton, CA, or SDI, Camp Lejeune, NC, (from here highlighted in original post, R.) or have held either MOS 0311, 0313, 0331, 0341, 0351 or 0352 upon selection to staff sergeant.(END highlighting, R.)
Duties: For a complete listing of duties and tasks, refer to NAVMC Directive 3500.87, Training and Readiness Manual.
Related Department of Labor Occupation Codes :
Infantry Unit Leader 378.137-010.
Related Marine Corps Jobs:
None.
Above information derived from MCBUL 1200, parts 2 and 3
(As you can see by the highlighted section, if you make SSG while in a qualifying MOS, you need not attend the school as you will have learned all that is needed via OJT)
Good Luck & Semper Fi!