Objectives: The Gradual Increase Length and Complexity of Utterance (GILCU) therapy method is a form of operant conditioning. This is a precise and controlled treatment that is done in 54 steps in 3 speech situations consisting of monologue, reading, and conversation. This study aimed at examining the effects of GILCU treatment method on the reduction of speech dysfluency of school-aged children with stuttering. Methods: In this quasi-experimental study, 32 children with stuttering (6-11 years old) who were referred to speech therapy clinics were selected using convenience sampling. Then, they were assigned into two groups. The first group was treated by GILCU therapy method by the researcher, and the second group was treated by traditional methods by another speech therapist. Both groups had fourteen 45-minute sessions that were conducted one to two times per week. Pre-test and post-test of both groups were assessed using the SSI-3 scores. The obtained data were analyzed using the Kolmogorov-Smirnov, t-test, and covariance test. Results: Both groups had statistically significant difference (P<0.005) in the stuttered syllables frequency. The average of moments of stuttering from the maximum moments of stuttering and the physical activity were examined according to the speech situations such as reading and conversation. The first group (GILCU therapy method) did not show any statistically significant improvement (P>0.005) with respect to parameters of SSI-3 scores. Discussion: These results suggest that a non-programming treatment for stuttering may be effective with school-aged children who stutter.