We examined the effectiveness of a psychosocial intervention in reducing mental health symptoms among war-affected children, and the role of peritraumatic dissociation in moderating the intervention impact on posttraumatic stress symptoms (PTSS). School classes were randomized into intervention (n = 242) and waitlist control (n = 240) conditions in Gaza, Palestine. The intervention group participated in 16 extracurriculum sessions of teaching recovery techniques (TRT) and the controls received normal school-provided support. Participants were 10- to 13-year-old Palestinian girls (49.4%) and boys (50.6%). Data on PTSS, depressive symptoms, and psychological distress were collected at baseline (T1), postintervention (T2), and 6-month follow-up (T3). Peritraumatic dissociation was assessed only at baseline. Regression analyses that took regression to the mean and cluster sampling into account were applied. The results on intervention effectiveness were specific to gender and peritraumatic dissociation. At T2, the intervention significantly reduced the proportion of clinical PTSS among boys, and both the symptom level (R2 = .24), and proportion of clinical PTSS among girls who had a low level of peritraumatic dissociation. The results have implications for risk-specific tailoring of psychosocial interventions in war conditions.