My 13-year-old, who'll be entering eighth grade, has always been a high achiever. In the middle of seventh grade he met up with a new friend - and since then he has gotten into trouble a few times. His grades have gone from A's to low B's and even low C's. His new friend is probably not going to pass the seventh grade. I don't want to try and stop this friendship -- should I just encourage my son to get better grades?
You are probably dealing with a combination of age- and friend-related issues. At age 13, boys are reaching puberty and experiencing all of the hormonal and independence issues that go along with that. It also begins to be "cool" to not be a high-achiever in school, and some children who were excellent students before may begin to slide.
Since you don't want to stop your son's friendship, perhaps you could encourage your son to do things with other people. Have something else planned when you think the boy may want to do something with your son, or help your son find some new friends in the neighborhood, at a computer camp, or through a YMCA.
Talk with the principal at your son's school. The problem may resolve itself if the other boy has to repeat seventh grade, but in case he is promoted, ask the principal to place the two boys in different classes or on different teams. If the other boy is retained, your son may realize that being friends with him will only be a problem and the friendship may cool on its own.