Yes, assessed values are based on the supposed market value of a house, BUT the tax RATE or a special assessment are tools a town could use to get more tax out of homeowners. There are always other ways to get money from taxpayers - increasing rates for Water and Sewer for one.
With that said, let's face it, the taxpayers of this great country paid for this school as well. Newton got a great deal of Federal and State grants to help pay for the school. In 2007 Newton schools received about $10M in State and Federal grants just on general principle. I know they got a huge chunk for the High School when they first proposed it. Don't remember how much that was though...might have to look that up!
Newton and Brookline are my specialty and I have no knowledge of the planned property tax increase. Of course, when it comes to taxes things have a tendency to change every year, so I don't know how useful it is to worry about it :)
On the other hand, it is a good thing for the neighborhood to have such a project! Of course, after the construction is over :)... I'd be thinking more about what really matters to me in a particular location and how to make it work $-wise or, if I cannot afford it, look for another location, with similar 'matters', that I can afford. I know both Newton and Brookline do not come cheap, yet there are always workable solutions or compromises that can be well worth it.
This is a fabulous website where you can speak directly with people who have children (or live in) the school systems so you might get better feedback.
Here is every property for sale in Newton:
Here is every property for sale in Brookline: