I think Cheerilee and the whole school aspect runs deeper than we perceive there was probably a time where there never was a school in Ponyville to begin with and Ponies were just thrown into the world with no guidance or help causing a lot of introspective turmoil and confusion as to what there purposes in life were. The only pony who apparently saw the damage that was happening to these depressed fillies was Cheerilee you could even go as far to say that she helped some of her close friends realize there talents which gave her the incentive to help all the fillies, but of course not all the fillies comprehend this crucial aspect such as this famous quote and no pun intended "You can lead a horse to water (but you can't make it drink)."
Which explains the Cutie Mark Crusaders there has been plenty of foreshadowing as to what there special talents are but they have been blinded and corrupted by Diamond Tiara & Silver Spoon's(DT&SS) constant harassment to the point were they have lost the connection of what it TRULY means to have a Cutie Mark, its not something that you flaunt and parade through the town with making everypony feel inferior to you, NO!
Taking a step back to Cheerilee yes you could say she is a teacher but I think she is a Motivational Speaker cleverly disguised as a school teacher (to make a better connection with younger audiences.) I only say this because there hasn't been any instances where they are doing school work no mention of homework from Applejack nor Rarity but of course just cuz we cant see it means we cant say it doesn't exists!! back on track she can only do so much to drive the fillies in the right direction but the fillies themselves are the only key to unlocking and finding there talents resulting in a Cutie Mark!!
For instance Twist and Applebloom they both got bullied by DT&SS yes? Applebloom let it get the best of her as for Twist just simply just brushed it off not letting it interfere with her in the end who got there Cutie Mark first? Twist because she stayed positive, kept a smile, and kept moving through thick and thin!! My point being is Cheerilee uses Motivational Speaking to encourage them to seek out there special talents and the school is represented in a different way yes they go there to learn but they learn in a completely different way than what humans are use to, if they cant understand what it means to have a Cutie Mark maybe they don't deserve one...?