I think everybody likes to talk about themselves - so the best thing to do when you run out of things to say is to ask questions!
Ask about their plans for the summer, or for holidays. Ask them questions about hobbies they have expressed interest in. (Ex: "I remember you said you liked racquetball? How long have you been playing? Where did you learn? Is it hard?")
You can help the HubPages community highlight top quality content by ranking this answer up or down.