Thanks to scientists who have ventured outside the laboratory, we have learned that tight-knit groups of females experience synchronized menstrual periods over time, that cohesive groups engaged in decision-making discount dissenting viewpoints in the interests of consensus, and that couples who stay together long enough begin to look alike. In the wilds of a New York City biology classroom, a new study has captured another group phenomenon known to exist in labs but never before chronicled in humans' natural habitat: group brain synchrony. Psychology researchers at New York University equipped each of 12 high school seniors with a portable, low-cost electroencephalogram and gathered the gadgets' brain-wave readings over a semester's worth of biology classes (11 sessions lasting 50 minutes each). Writing in the journal Current Biology, the researchers reported that when students were most engaged with each other and in group learning, the readings on their electroencephalograms, or EEGs, tended to show brain-wave patterns that rose and dipped in synchrony. That neural synchrony was most pronounced when students reported they liked their teacher.