That is a very naive take. First, the trust in crypto is extraordinarily expensive, as Budish's famous "The economic limits of Bitcoin" paper shows.

Second, the crypto bros running Bitcoin have reverted 20+ blocks on at least two occasions when it suited them to do so, and Ethereum has famously undone the DAO hack. Oh, and then of course you have all the bugs in smart contracts that can't be fixed. So the notion that "code is law" is laughable, and the notion that it's desirable is misguided, too.

Third, there's the oracle problem. Keeping track of bits in a ledger is a solved problem and has been a solved problem for a long time. The issue is correlating it with the real world. In your example, what if the student pays, then the teacher doesn't teach? How is the money flow reverted? If the student can just revert it, what happens if the student pays, the teacher teaches, and the student then reverts the payment? You need the legal system, and external adjudication, one way or the other.

Crypto adds nothing but idle speculation and the circumvention of (largely sensible) rules and regulations.