J.K. FAQ 40 oficial do site da Web de Rowling
Q: Can prefects take points or not? A prefect took points from Gryffindor in the Chamber of Secrets, and then there was a reference to prefects not being allowed to dock points. What are the rules?
Answer: Ron got it wrong in 'Phoenix', from which we deduce that he hasn't been a very authoritarian prefect thus far; he clearly hasn't been taking points from anybody.
link A seção "Nos bastidores" declara:
There was some confusion about the point-taking ability of prefects after the original release of Harry Potter and the Order of the Phoenix. It had previously been stated in Harry Potter and the Chamber of Secrets that prefects could dock points, but in a scene in the first printing of Harry Potter and the Order of the Phoenix Ron Weasley, Ernie Macmillan, and Draco Malfoy all either state outright or imply that prefects are not allowed to take points. This was pointed out as a mistake, and subsequent printings had a slightly different version of the dialogue, making it clear that prefects can take points, just not from other prefects.