Chicago Mayor Rahm Emanuel recently incurred the wrath of the city’s teachers’ union when he lengthened the elementary school day, starting next year, to seven and a half hours from less than six. One can only imagine that when those kids finally bust free, they’ll be 90 minutes crazier than schoolkids are everywhere on weekdays come 3 p.m.-ish. And that final-bell madness can extend to parents and nannies picking them up. “It’s a challenging time of day because everyone is tired and people want to get home, but often children have stories to tell about what happened that day,” says George W. Holden, a psychology professor at Southern Methodist University in Dallas and author of Parenting: A Dynamic Perspective. Recently, Bloomberg Businessweek observed school pickup at five top elementary schools in the New York area—the Upper East Side’s Dalton School, the Upper West Side’s Ethical Culture Fieldston School, Greenwich Village’s P.S. 41, Tribeca’s P.S. 234, and Park Slope’s P.S. 321 in Brooklyn. Then we ran our impressions by Holden and three other experts: Patti Wood, author of the forthcoming Snap: Making the Most of First Impressions; Joe Navarro, author of What Every Body Is Saying; and Adam Mansbach, parent of a pre-K’er and author of the cult-hit “children’s” book Go the F- - - to Sleep. Here is our semi-scientific taxonomy of school pickup behaviors and what the pros think they mean. Brace yourself, Windy City.