Improvement over 12 months of two groups of Portuguese preschoolers is analyzed after a parental intervention with the Incredible Years Basic Parent Program (IY). The groups were defined by the children’s initial levels of hyperactive behaviors (high hyperactivity, n = 34; low hyperactivity, n = 18). Changes in the children’s reported hyperactive behaviors and in mothers’ self-reported parental practices and mood were evaluated from baseline to the 12-month follow-up. Preschoolers with higher initial hyperactivity levels seem to have benefitted more from the IY intervention compared to children with lower baseline levels. However, this low-hyperactivity group improved as well. Findings also indicate high levels of maternal acceptance and satisfaction with the intervention in both groups, although some differences were observed. Overall, findings suggest that IY is equally suitable for parents of Portuguese preschoolers with high- and low-hyperactive behaviors at baseline, highlighting the usefulness of the program for children with different risk levels.