We examined relations between salivary cortisol, alpha-amylase (sAA), and children's cognitive and academic functioning. Of interest were curvilinear and interactive effects of these salivary measures on cognitive and academic performance. Data were based on a sample of 28 boys and 36 girls (ages 8 and 9) in the Southeastern U.S.A. Children provided resting afternoon saliva samples. Children completed standardized tests of Intellectual Ability and schools provided academic achievement information. Regression analyses demonstrated significant curvilinear relations and interactions between cortisol and sAA in the prediction of child functioning. Contrary to current models of interactions among biological systems, findings indicated some of the highest and lowest scores were predicted at moderate levels of physiological arousal. For example, children with moderate sAA and either higher or lower cortisol had low predicted scores for Reading Ability. Children with moderate cortisol and lower sAA had the highest predicted scores for Intellectual Ability. Findings suggest that the study of interactions between biological stress response systems should not be based on models of rectilinear interactions.