We document and analyze the emergence of a substantial gender gap in mathematics in the early years of schooling using a large, recent, and nationally representative panel of US children. There are no mean differences between boys and girls upon entry to school, but girls lose more than...

The "Hawthorne effect" draws its name from a landmark set of studies conducted at the Hawthorne plant in the 1920s. The data from the first and most influential of these studies, the "Illumination Experiment," were never formally analyzed and were thought to have been destroyed. Our research has...