Objective: The present study utilized ecological momentary assessment (EMA) to examine the effects of emotional impulsivity on overall functional impairment and functional impairment variability (FIV) of children with and without ADHD. Method: Parents of 74 children, 8- to 12-year-olds (42 with ADHD, 32 without ADHD), completed EMA assessment protocol ratings of their child’s mood (3 times daily) and functional impairment (1 time daily) over the course of 28 days. Results: Hierarchical regression analyses supported the interaction of ADHD diagnostic status and greater EMA-derived emotional impulsivity in the estimation of total functional impairment (Total FI) and FIV. Thus, greater emotional impulsivity was found to be related to greater Total FI and FIV among children with ADHD but not among children without ADHD. Conclusion: This study suggests that children with ADHD and greater emotional impulsivity demonstrate greater overall levels of functional impairment, with the severity of their impairment varying significantly over time.