The purpose of this study is to examine how respiratory sinus arrhythmia (RSA) is affected across paced breathing, attention, inhibition, and emotion-eliciting tasks and how those relationships may be mediated by emotion regulation strategies in children with different levels of externalizing and internalizing behaviors between the ages of 8 and 12 years. The first aim was to determine whether externalizing and internalizing symptoms during a paced breathing or natural breathing task better predicted RSA levels. The hypothesis was that internalizing and externalizing behaviors would be more predictive of RSA baseline levels when utilizing a paced-breathing method of measuring RSA. The second aim was to determine how RSA levels across an attention, inhibition, sad, and anger task are predicted by internalizing and externalizing symptoms after controlling for baseline RSA levels. There were four hypotheses: (1) as levels of externalizing behaviors increase, levels of baseline RSA would decrease, (2) as levels of internalizing behaviors increase, levels of baseline RSA will decrease, (3) there will be significantly smaller changes in RSA reactivity) as the level of externalizing behaviors increases, and (4) as levels of internalizing symptoms increase, there will be significantly larger changes in RSA levels relative to RSA baseline levels (RSA reactivity).The results showed that externalizing and internalizing behaviors did not predict RSA levels during a paced or natural breathing task. Additionally, there was very little difference in the outcomes when used either a natural or paced breathing method of RSA as a control variable except when predicting RSA levels during a sad emotion-eliciting task. Although RSA levels during three experimental tasks (attention, inhibition, and sad) were not significant, there were moderate effect sizes for externalizing and/or internalizing symptoms predicting various RSA reactivity (i.e., RSA levels after controlling for baseline) across these conditions. One model was significant in predicting the level of variance of RSA reactivity during an anger emotion-eliciting task, with internalizing and hyperactivity/inattention symptoms contributing the most variation in the model. Findings point towards understanding how internalizing and externalizing symptoms may impact an individual's physiological response during a task.