Fourteen-year-old Milo Beckman did some great research to determine that longer SAT essays get higher scores. His finding are backed up by an MIT researcher who has found that length accurately predicts score 90% of the time. BONUS: Milo considered causality. He determined that length is actually what’s causing the higher score. It’s not just that better writers write more! Go Milo!
P.S. Since the GRE is a close cousin to the SAT and the essays are graded in a similar manner, it wouldn’t hurt to write more on the GRE essays as well!