With the price of private-school education easily running to the tens of thousands of dollars each year, it's no wonder many families will only look at properties that fall within a coveted school district. Public School 321 in Park Slope is one institution that inspires such fervid real-estate loyalty, and it's probably a big reason the Brooklyn neighborhood is so overrun with kids. It can't hurt that its leafy streets are lined with handsome brownstones and gracious co-ops — and, increasingly, modern condos — that offer plenty of space for a little bit less than what you'll pay in Manhattan. Alas, they used to cost a lot less. —S. Jhoanna Robledo