Peace is a matter of negotiations. And besides a big compromise it contains also many detail solutions. That makes it very difficult to impose peace because an outsider cannot be aware of all those details.
A good illustration of this is education. After Dayton in Bosnia each ethnic group had for eight years its own education. Specially history was a subject where each group had its own vision. Only then did they reach a compromise that did not offend any of the ethnicities.
The Ahtisaari plan is rather short on education in Kosovo. The minorities have the right to education in their own language. But for the rest the government is free to do what it wants. So if Ahtisaari has his way there will be no educational compromise in Kosovo like in Bonsia, but instead the Kosovo's government will be able to impose the Albanian vision on the Serbs. And past experience learns us that they are prepared to close schools to enforce the obedience to that vision.
Then there is the problem of higher education. In the past Kosovo's government has tried to introduce a law that offered ony higher education in Albanian. It was vetoed by the internationals. But given the small size of the Serb community it is clear that only the most popular subjects can be offered in Serbian in Kosovo. For the rest people will have to go to Serbia. As few Serbs in Kosovo speak fluent Albanian higher education in Albanian is no option for them.
As I have written more often: to solve ethnic problems both sides should sit as equals on the negotiation table. This kind of mutual respect lacks at the moment between Kosovo's Serbs and Albanians. Ahtisaari made the problem only worse as he didn't have that kind respect himself. The problem with education is but one of many problems that his one-sided solution produced.