The single programmatic change that would make the largest difference for students in poor school districts in the United States would be abolishing summer vacation.
The second would be lengthening the school day. And, no, improvements in learning outcomes and overall well-being would not be limited to the poorest districts.
The most important benefit of public schools for most students - whether they are rich or poor - is that it keeps them away from dysfunctional families and dysfunctional neighborhoods for at least 35 hours per week, 40 weeks per year. (There's surprisingly little evidence that schools are effective at teaching anything aside from basic literacy and basic numeracy, and there are plenty of high school graduates in the United States who aren't even getting that much.)
Out of curiosity, do you support the traditional incarnation of "year-round schedules" in lieu of a summer vacation? My cousins went to a public school district with a year-round schedule and they had a month off during summer and 2 weeks off during every other season (plus a week for Thanksgiving). Or do you favor abolishing weekly breaks altogether in order to increase days in school per year to 220+?
