I don't know the financial details of PPP road projects but i agree its hard to see how makes financial sense for the government in the long term. Easy to see why makes sense financially in the short term.
Again don't know the figures for the school PPP but they would seem to make sense. The private company builds & maintains the building, by having numerous schools in its portfolio the private company can make cost savings. The state sticks to what it does best which is education. In fact this would be good model for hospitals too.