This groundbreaking study of girlhood and cognition argues that early moderns depicted female puberty as a transformative event that activated girls' brains in dynamic ways. Mining a variety of genres from Shakespearean plays and medical texts to autobiographical writings, Caroline Bicks shows how 'the change of fourteen years' seemed to gift girls with the ability to invent, judge, and remember what others could or would not. Bicks challenges the presumption that early moderns viewed all female cognition as passive or pathological, demonstrating instead that girls' changing adolescent brains were lightning rods for some of the period's most vital debates about the body and soul, faith and salvation, science and nature, and the place and agency of human perception in the midst of it all.