In elementary school, you're told to make new friends, but keep the old. But how many of us actually remember actively putting in an effort to make those friends? Playdates were usually set up by our parents, and our friendships were usually a result of who was in our classes.
In middle school, things got cliquey and your social status was determined by how many bar and bat mitzvahs you got invited to (at least, that was the case where I grew up). You worried about who you would sit with in the cafeteria, and whether or not it was actually cool to be in the school band or chorus.