Joel Spolsky recently spoke at Y Combinator about selling software to corporate customers. He said that in most companies software costing up to about $1000 could be bought by individual managers without any additional approvals. Above that threshold, software purchases generally had to be approved by a committee. But babysitting this process was so expensive for software vendors that it didn't make sense to charge less than $50,000. Which means if you're making something you might otherwise have charged $5000 for, you have to sell it for $50,000 instead.
The purpose of the committee is presumably to ensure that the company doesn't waste money. And yet the result is that the company pays 10 times as much.
Checks on purchases will always be expensive, because the harder it is to sell something to you, the more it has to cost. And not merely linearly, either. If you're hard enough to sell to, the people who are best at making things don't want to bother. The only people who will sell to you are companies that specialize in selling to you. Then you've sunk to a whole new level of inefficiency. Market mechanisms no longer protect you, because the good suppliers are no longer in the market.
These are pretty good reasons for why schools get such crappy software. Also, note that other large enterprises have the same problem. Teachers have a tendency to come up with overly philosophical reasons to explain why their schools seem so poopy. A lot of it is just that they're big enterprises. Working for a big business is often equally poopy.