Inconsistent parental discipline is a robust correlate of child attention-deficit/hyperactivity disorder (ADHD) symptoms, but few studies have considered the role of inconsistent "positive" parenting on ADHD, as well as the effects of stress on negative and positive parental consistency. This study advanced a novel ecological momentary assessment (EMA) using participant smartphones to measure parental consistency, and examined its associations with family, social, and parenting-related dimensions of stress and child ADHD symptoms. Participants were 184 kindergartners with and without ADHD and their parents. Harsh and warm dimensions of parental behavior were assessed using questionnaires, observations, and an EMA administered through parents' smartphones, which measured parent-child behaviors every day for a period of 1 week. Family, social, and parenting-related stress were assessed from questionnaires, and child ADHD symptoms were assessed from a fully structured diagnostic interview with the parent. Child ADHD symptoms were associated with variability in warm parenting behaviors, and higher levels of parenting-related stress were related to greater variability in harsh parenting behaviors. No significant interactions were detected between parental stress and child ADHD on parental variability. These findings suggest that different factors influence the "consistency" in parenting behavior, depending on whether positive parenting or negative parenting is assessed. Parent-based treatment programs for children with ADHD should include a stronger focus on reducing stress from parenting (e.g., teaching coping skills for parents), as this may lead to greater consistency in parental behavior more generally, and presumably better child outcomes.