I was just wondering about something. In chamber of secrets Percy takes points from Gryffindor because of Ron.
"Five points from Gryffindor!" Percy said tersely, fingering his prefect badge. "And I hope it teaches you a lesson! No more detective work, or I'll write to Mum!"
However in book 5 there is a confrontation between Malfoy and Harry in which the following is said:
ʹItʹs only teachers who can dock points from houses, Malfoy,ʹ said Ernie at once. ʹYeah, weʹre prefects, too, remember?ʹ snarled Ron. ʹI know prefects canʹt dock points, Weasel King,ʹ sneered Malfoy. Crabbe and Goyle sniggered. ʹBut members of the Inquisitorial Squad ‐ʹ