Objective: An earlier meta-analysis of pediatric clinical trials indicated that lisdexamfetamine dimesylate (LDX) had a greater effect size than other stimulant medications. This work tested the hypothesis that the apparent increased efficacy was artifactual. Method: The authors assessed two potential artifacts: an unusually high precision of measurement and an unusually low placebo effect. The authors evaluated generalizability from children of adults. Results: The LDX effect sizes for children were significantly larger than the pooled stimulant effect sizes from studies using the same outcome measures. However, although no other individual stimulant study had an effect size greater than LDX, there was overlap between the 95% confidence intervals for some of these studies and the LDX study. The high LDX effect sizes were not due measurement or placebo effect artifacts. LDX effect sizes for adults were not larger than the stimulant effect sizes from other studies. Conclusion: The high LDX effect size for children could not attributed to measurement artifacts. The superiority of LDX in the pediatric clinical trial reflected the greater efficacy of amphetamine products, compared with methylphenidate products but required replication in children because (a) the results were based on only one trial of LDX in children, and (b) the finding did not generalize to adults. (Contains 5 figures and 2 tables.)