The present study examined quantitative and qualitative factors related to the effectiveness of a behavioral regulation intervention using classroom games with 65 prekindergarteners. Previous research indicated that participation in an intervention was related to behavioral regulation gains for children who started the year with low levels of these skills and significant letter-word identification gains for all children in the intervention (Tominey & McClelland, 2011). Children from low-income families experienced smaller intervention-related gains than their peers. In the present paper, we examined how child and family factors predicted children's initial levels of behavioral regulation. Additionally, we analyzed qualitative fieldnotes looking for behaviors that could explain the reduced intervention effects experienced by children from low-income families. Results of a logistic regression indicated that maternal education significantly predicted behavioral regulation at the beginning of the prekindergarten year. Moreover, qualitative analyses revealed relations between off-task behaviors exhibited during intervention sessions (including spillover effects) and children's family income level. Findings underscore the importance of targeting children from low-income families and those with low levels of maternal education for behavioral regulation interventions. Implications for future applications of the intervention include increasing the number of intervention sessions and embedding behavioral regulation activities into prekindergarten classrooms. (author abstract)