Parents and Children Making Connections – Highlighting Attention (PCMC-A) is a dual-generation intervention program for families from lower socioeconomic status backgrounds that includes parenting training for parents and attention training for preschool-aged children. PCMC-A has been shown to impact brain function for selective attention in children, the ability to enhance relevant information and suppress competing, distracting information. With the goal of increasing our understanding of how PCMC-A operates to promote gains in child brain function for selective attention, the main objective of this dissertation was to test intervention-related changes in supportive parenting behaviors as an explanatory mechanism for the effect of PCMC-A on neural indices of selective attention. To better understand the profile of those who benefit from PCMC-A to different extents, we also examined moderators of the effect of PCMC-A on supportive parenting and on child brain function for selective attention. These questions were examined as part of the randomized controlled trial to evaluate the impact of PCMC-A on Head Start preschoolers and their parents, employing a multi-method approach. We found that participation in PCMC-A led to increases in specific aspects of supportive parenting behaviors coded from observed parent-child interactions, which were moderated by child and mother characteristics at the pre-assessment, including mother reports of child behavior problems, child age, and maternal interactive language use. We also replicated with a larger sample an effect of PCMC-A on child selective attention measured using the event-related potential technique, which was moderated by mother reports of child social skills at the pre-assessment. Even though we documented changes in both of these outcomes as a function of PCMC-A, we did not find evidence that changes in supportive parenting explained gains in child selective attention, suggesting that other explanatory mechanisms may be at play. Together, the findings of the present dissertation characterize the effect of PCMC-A on supportive parenting behaviors and child selective attention, begin to paint a picture of the families who benefit most and least from this intervention, and contribute to our understanding of the mechanisms through which PCMC-A impacts child brain function for selective attention. This dissertation includes unpublished co-authored material.