Last month, just before the new school year started in Japan, I ran into a neighbor at the supermarket. She's a bit high-strung and gets worked up over school matters, so I try to avoid her. But she collared me by the cabbages and dropped her voice to a dramatic whisper. "Have you heard? The Suzukis were transferred to Sendai! If any more kids move away, we won't have enough sixth-graders this year!"

I knew exactly what she meant. Parents at our school keep a close count on the number of students, and head count is a big topic of conversation in March. That's when company employees get their transfer orders and families move in and out of the school district. My neighbor was worried that the number of students entering sixth grade would drop below 41 before the beginning of the school year. If it did, the school would have to put her daughter and all the other sixth-graders in one huge class.

That's because the central government sets maximum class size and decides how many teachers a school can have. For many years, the Education Ministry has strictly enforced a "40 kids per class" rule, which works like this: Let's say a school has 81 incoming first-graders. This group could be divided into three classes of 27 students each, and the school would be allocated three teachers for first grade. But what if there were just one child fewer? Then there could only be two first-grade classes, each with 40 students. The school would only get two teachers for that grade.