This paper discusses the impact of emerging developmental skills on preschoolers' test performance in reference to preoperational thinking, behavioral controls, and language skills. It is emphasized that some behaviors that occur during the preschool period may suggest pathology when observed in older children but are normal for preschoolers. A Piagetian model is used to conceptualize how the preschooler's behavior can influence test outcomes. Specific strategies for eliciting a better test performance are described in reference to the following problems: reactions to failure, overreactivity and distractibility, negativism and oppositional behavior, and perseverance on old tasks or manipulation to avoid new tasks. (Author/SS)