It is fairly well established that poor kids in schools that are not majority poor, do significantly better in school than poor kids who are warehoused in schools full of poor kids. This may have something to do with self-selection. Parents who care enough to use school choice to put their kids in more affluent schools may be more involved. But, it also likely has a lot to do with expectations from teachers, role models, and an atmosphere where most of time, the school is operating in the environment for which the curriculum and system was designed.
Of course, this is a tall order in a city like Denver, where a majority of the kids are poor and the school district has no ability to make anyone attend a school other than their home school, now that desegregation orders have ended.