College + Game Design = A skill system that mimics degree progression....

Game concept with skills that mimic college degree progression. Duel major, bachelors, associates, masters in education, masters in a subject. Academic regalia for gear/style.

In order for a character to gain levels in a class (“major”) they must complete certain missions in the academy. Completing missions offers progression. When you have completed all the missions you may use that class out of the academy.
Academy missions are fun and teach/reinforce basic concepts of game-play elements the character needs to play in that style. (Teach tanks to kite for example and rogues to interrupt reliably if we were using WoW raiding for example) This should be tailored to include expectant emergent gameplay as well if at all possible.
There are a finite number of academy missions. Many classes take the same missions. Missions work much the same way that classes at a university work. Certain missions are only offered at certain times of day (for example- a mission that teaches “stealth” would only be at night!)

Example Academy Missions
Core
-Basic Movement: This teaches you the basics of movement. You listen to a tutorial before you have to demonstrate the ability to do it.
-Basic Jumping & Falling: This teaches you how to jump and about fall damage. The players must jump up a series of ledges.
-Basic Combat: This teaches you the basics of combat. It includes how to select a target, how to attack, how to resurrect, how to attack. Players must dish out the pain against a room full of dummies.
-Advanced Combat I: You learn how to use skills in combat and are pitted against a series of different enemies to broaden your pallet. Enemies include, a single melee enemy, a single ranged enemy, a swarm of weak melee enemies, a swarm of weak ranged enemies, and an elite enemy.
Stealth
-Basic Stealth Training: You must listen to the tutorial for “stealth mode”. Stealth mode allows you to remain undetectable by NPCs (and players) while in areas with a relatively lower light value than the sounding area.
-Stealth Training II: You must successfully navigate a long hallway with guards in a limited timeframe, grab an object at the end of the hallway and bring it back. This also shows that you can’t move quickly while carrying a heavy object.
-Double Jump Training: You learn how to air jump using the “Double Jump” class feature. A series of moving ledges with enemies try to preclude you from reaching your objective against the time limit!
Ranged
-Ranged Combat I: After a brief tutorial you are challenged to shoot several rising balloons at the mercy of the wind!
-Ranged Combat II: You are taught about ranged skills and anti-air unit techniques.