In a world filled with terms like “value-added” and “adequate yearly progress,” many parents still rely on a far simpler data point to assess a school’s quality: the number of students in the classroom. They feel, strongly, that their child stands to get more personal attention in a class of 17 students than in one of 27 and that smaller classes are less likely to get out of hand. According to a 2007 poll in the journal Education Next, more than three-quarters of parents would rather shrink classes than pay teachers more.

Smaller classes are wildly popular among teachers, too, for similar reasons. They say that with fewer students, they can control them better, give more personal attention, and assign and grade more complex work. Nadia Zananiri, who has about 35 students in her Advanced Placement world history class in Miami Beach, Fla., says, “Something is going to have to give . . . You can only humanly grade so many essays. This is a writing-heavy class, so the options are to assign fewer assignments or give less feedback.”

Yet with only limited research bolstering the case for class-size reduction, legislative mandates are fizzling out, and the topic has been all but dropped from public debates about how to improve schools.