It is known that operant treatments can control stuttering in children. However, at present it is unknown why such treatments are effective. Changes in the usual way of speaking are frequently observed after behavioural treatments for adults who stutter, and it is possible that operant treatments for children also invoke such changes. To explore this idea, selected acoustic measures of speech timing were made in eight preschool children before and after receiving the Lidcombe Program, which is an operant treatment for stuttering. No systematic changes were detected after treatment. Considering this finding and a previous report, there is no evidence to suggest that the reductions in stuttering that occur with this treatment are related to systematic changes in speech timing or curtailment of language function.