Abstract: Reliable laboratory protocols manipulating the intensity of biobehavioral arousal for children are uncommon, and those available have minimal converging evidence of their efficacy in manipulating arousal across multiple biological systems. This report presents two studies of the efficacy of the modified Trier Social Stress Test (TSST-M). In Study 1, sixty-three 7-15-year olds, and 19 young adults (18-25 yrs) completed the TSST-M. Comparable reactivity across age groups was observed for salivary cortisol, salivary alpha-amylase (sAA), pre-ejection period (PEP) and respiratory sinus arrhythmia (RSA), whereas self-reported stress was higher in adults compared to children. In Study 2, eighty-four 7-8-year olds and eighty-six 12-15-year olds were randomly assigned to a standard or low-stress TSST-M condition. Cortisol and self-reported stress responses were higher in the standard compared to the low-stress condition. In contrast, sAA and PEP were higher in the low-stress condition and RSA responses were comparable between the two TSST-M conditions. In addition, age group differences emerged in Study 2, though never in conjunction with the TSST-M manipulation. To test, refine, and advance theory about the implications of stress for child development, laboratory tasks that manipulate and enable assessment of biobehavioral arousal in children are needed.