There are 2 phases to this trial. In Phase I the child will receive 1 of the following 6 treatments for 12 weeks: 1) SER alone; 2) pill PBO alone; 3) CBT alone; 4) SER plus CBT; 5) SER plus ES; 6) pill PBO plus ES. If the child responds to treatment, he/she will go on to Phase II in which the treatment will be slowly reduced, then stopped (discontinued), over time to test the treatment's durability. The child will be evaluated at Weeks 1, 4, 8, 12 (Phase I treatment), and Weeks 16, 20, 24, and 28 (Phase II discontinuation) to see how effective and durable the treatment is in treating your child's OCD.