Sounds like a nice idea, but isn't feasible. Imagine you paid a student school fees of $5,000 a month ago with steem, and another person pays that same amount with steem today. There will be a difference of over $1,000. That's due to volatility.
The high volatility of most cryptos would be a challenge. The prices fluctuates with time, only pegged coins are exceptions. That's because both the retail market and institutions (universities included) are not very sure about about it.
Another challenge would be how people perceive it. Cryptos are not widely adopted yet. Some people think it’s not real money, or that it's associated with buying illegal stuff online. So such parents or guardians would find it hard to pay school school fees with what they feel isn't real or illegal. The way people use it for ponzis and scams have also had adverse effects on adoption.
The most popular crypto, Bitcoin, though being around for many years, is still in early phases. Other cryptos too, like our beloved steem and steem dollars are not left out. Cryptocurrency being unregulated, frightens most people. And fear is usually not a good thing.
It might take a while for cryptocurrency to be introduced in the payment of school fees at educational institutions. But it'll happen.