Detection of early risk for developing childhood attention-deficit/hyperactive disorder (ADHD) symptoms, inattention and hyperactivity, may be critical for prevention and early intervention. Temperament and parenting are two promising areas of risk, representing potential targets for preventive intervention; however, studies have rarely tested these factors longitudinally using multiple methods and reporters. In a longitudinal sample of 312 low-income boys, this study tested the hypothesis that negative emotionality (NE) and effortful control (EC) in toddlerhood (1.5–3.5 years old) would predict mother- and teacher-reported ADHD-related behaviors at school age (5–7 years old). Direct effects of observed warm, supportive and harsh maternal parenting were tested in relation to ADHD-related behaviors and as moderators of associations between NE and EC and ADHD-related behaviors. Several predictions were supported: 1) Greater maternal-reported toddler NE positively predicted mother-reported ADHD behaviors; 2) Greater observed EC was associated with fewer mother- and teacher-reported ADHD-related behaviors; 3) Warm, supportive parenting predicted fewer teacher-reported ADHD-related behaviors, and harsh parenting predicted more ADHD-related behaviors as reported by parents and teachers; 4) Harsh parenting moderated the association between observed EC and mother-reported ADHD-related behaviors. Together, the findings suggest that lower child EC, lower warm/supportive parenting, and greater harsh parenting in toddlerhood independently signal increased risk for later ADHD-related behaviors; further, the association between low EC and ADHD-related behaviors was amplified in the context of high levels of harsh parenting.