Having done that, get another load of people to bang on every door in the 50 neighbourhoods in the treatment arm, and offer them money to replace their windows and their soil. (I don't know whether you can get away with not replacing windows & soil for the residents who don't have kids in the study. If you could skip them you'd save a lot of money.) Then do the cleanup jobs.

A study sort of like this was done in Rochester, and they found that nothing they did changed blood lead levels very much and so they didn't learn anything from it. I guess they could go further with actually replacing people's houses.