Objective: This study aimed to characterize clusters of children based on ADHD and sensory over-responsivity (SOR) symptoms, and to compare their markers. Method: Parents of 922 infants completed the Infant–Toddler Social and Emotional Assessment (ITSEA) Sensory Sensitivity, Attention, and Activity/Impulsivity scales at three time points during early childhood and the Child Behavior Checklist (CBCL) and SensOR inventory during elementary school age. Results: Four school-age clusters emerged from the CBCL ADHD and SensOR scores: (a) elevated SOR symptoms only (n = 35); (b) elevated ADHD symptoms only (n = 38); (c) elevated ADHD and SOR symptoms (ADHD + S, n = 35); and (d) low ADHD and SOR symptoms (n = 814). The SOR and ADHD + S clusters had higher early Sensitivity scores than the ADHD and Low clusters. The ADHD and ADHD + S clusters differed from the SOR and Low clusters in their early Attention and Activity/Impulsivity scores. Conclusion: SOR and ADHD symptoms occur independently and consistently over time.