It does save on building construction costs, and often multi-track schools are in heavily populated cities. The calendar I was discussing originally was in a single-track school where all students and teachers follow the same calendar, and there are equal vacation times distributed throughout the year. This balanced calendar provides better education opportunities, and more than half the schools are on that calendar. Both types cut down on the long summer break that the research out of Johns Hopkins University shows has been instrumental in learning loss for inner-city students, in particular. And as far as being able to substantiate any educational advances in year-round students, there are none that are substantive.
Most studies show that students do better on balanced calendars than they do on traditional.
That's true, particularly in the math-science areas, where students have fewer educational opportunities over the long summer break. Our experience, in my school district, was far different. Most children do better with consistency. Summer school is not the same in that it provides remediation after failure. Inter-sessions can provide prevention throughout the school year.