Behavioral outcomes of intervention targeting young aggressive children have to be carefully assessed. Researchers and practioners need reliable, valid, and bias-free instruments that are also sensitive enough to detect any change in children’s behavior. The first goal of this article is to highlight limitations imposed by indirect measures of behavioral assessment with children exposed to an intervention. The second goal is to illustrate issues related to direct behavioral assessment using observation procedure. The different options for researchers and practioners regarding the choice of behavioral targets and observation settings are discussed.