David and Goliath: Underdogs, Misfits, and the Art of Battling Giants

of a difference. And there’s the right side, where doing more or having more makes things worse. 4
    If you think about the class-size puzzle this way, then what seems baffling starts to make a little more sense. The number of students in a class is like the amount of money a parent has. It all depends on where you are on the curve. Israel, for example, has historically had quite large elementary school classes. The country’s educational system uses the “Maimonides Rule,” named after the twelfth-century rabbi who decreed that classes should not exceed forty children. That means elementary school classes can often have as many as thirty-eight or thirty-nine students. Where there are forty students in a grade, though, the same school could suddenly have two classes of twenty. If you do a Hoxby-style analysis and compare the academic performance of one of those big classes with a class of twenty, the small class will do better. That shouldn’t be surprising. Thirty-six or thirty-seven students is a lot for any teacher to handle. Israel is on the left side of the inverted-U curve.
    Now think back to Connecticut. In the schools Hoxby looked at, most of the variation was between class sizes in the mid- to low twenties and those in the high teens. When Hoxby says that her study found nothing, what she means is that she could find no real benefit to making classes smaller in that medium range. Somewhere between Israel and Connecticut, in other words, the effects of class size move along the curve to the flat middle—where adding resources to the classroom stops translating into a better experience for children.
    Why isn’t there much of a difference between a class of twenty-five students and a class of eighteen students? There’s no question that the latter is easier for the teacher: fewer papers to grade, fewer children to know and follow. But a smaller classroom translates to a better outcome only if teachers change their teaching style when given a lower workload. And what the evidence suggests is that in this midrange, teachers don’t necessarily do that. They just work less. This is only human nature. Imagine that you are a doctor and you suddenly learn that you’ll see twenty patients on a Friday afternoon instead of twenty-five, while getting paid the same. Would you respond by spending more time with each patient? Or would you simply leave at six-thirty instead of seven-thirty and have dinner with your kids?
    Now for the crucial question. Can a class be too small, the same way a parent can make too much money? I polled a large number of teachers in the United States and Canada and asked them that question, and teacher after teacher agreed that it can.
    Here’s a typical response:
    My perfect number is eighteen: that’s enough bodies in the room that no one person needs to feel vulnerable, but everyone can feel important. Eighteen divides handily into groups of two or three or six—all varying degrees of intimacy in and of themselves. With eighteen students, I can always get to each one of them when I need to. Twenty-four is my second favorite number—the extra six bodies make it even more likely that there will be a dissident among them, a rebel or two to challenge the status quo. But the trade-off with twenty-four is that it verges on having the energetic mass of an audience instead of a team. Add six more of them to hit thirty bodies and we’ve weakened the energetic connections so far that even the most charismatic of teachers can’t maintain the magic all the time.
    And what about the other direction? Drop down six from the perfect eighteen bodies and we have the Last Supper. And that’s the problem. Twelve is small enough to fit around the holiday dinner table—too intimate for many high schoolers to protect their autonomy on the days they need to, and too easily dominated by the bombast or bully, either of whom could be the teacher herself. By the time we shrink to six bodies, there is no place to hide at all, and not enough diversity in thought and experience to add the richness that can come from numbers.
    The small class is, in other words, potentially as difficult for a teacher to manage as the very large class. In one case, the problem is the number of potential interactions to manage. In the other case, it is the intensity of the potential interactions. As another teacher memorably put it, when a class gets too small, the students start acting “like siblings in the backseat of a