Background: In 2004, a firework factory in a residential area of a large Danish city exploded. The children at the local school were screened for symptoms of posttraumatic stress disorder (PTSD) 16 months and 3½ years after the incident. A large proportion of the children still suffered from a substantial number of symptoms 3½ years after the incident. Thus, a treatment program designed to target PTSD symptoms in trauma-exposed children was established. Objectives: The first aim of this study was to provide preliminary evidence that a classroom-based psychosocial intervention program for children with posttraumatic stress would be associated with reductions in symptoms. The second aim was to evaluate the usefulness of the Darryl, a cartoon-based PTSD screening instrument. Methods: One hundred and eight children participated in the treatment program, all of whom fulfilled at least two out of the three DSM-IV PTSD symptom clusters. The children were screened for PTSD symptoms at baseline and 1 month after treatment using Darryl. Results: There was a statistically significant reduction in PTSD symptoms from pre-treatment to post-treatment. Furthermore, a logistic regression analysis revealed that being female, being young, and having a high PTSD score at baseline predicted a probable PTSD diagnosis post-treatment. Conclusion The present study provides preliminary evidence of feasibility and that the treatment program described may help to alleviate PTSD symptoms children with chronic PTSD symptoms. Furthermore, the results indicated that the Darryl instrument is a useful screening tool for assessing PTSD symptoms in this sample of children.