Purpose <p>Interventions for individuals who have used intimate partner violence (IPV) are typically delivered in group format and preclude participation of partners/coparents. This study utilized data from six community clinics in Connecticut that provided Fathers for Change (F4C), an individual IPV treatment for IPV use that allows for optional coparent participation. Previous findings from this statewide implementation study found that F4C was associated with reduced IPV. This study explored factors that could improve or detract from fathers’ participation and engagement in F4C.</p> Methods <p>Data from 181 fathers who began F4C were examined to investigate the association of having at least one joint session with a coparent, the fathers’ IPV risk severity, the fathers’ substance misuse, and the fathers’ race/ethnicity on their: 1) treatment motivation, 2) alliance with their therapist, and 3) treatment completion.</p> Results <p>Having at least 1 session with their coparent was significantly positively associated with all outcomes. IPV risk severity and race/ethnicity were not associated with any of the outcomes. Fathers’ alcohol misuse was negatively associated with their working alliance, while fathers’ drug misuse was associated with less treatment completion.</p> Conclusions <p>These findings suggest that, when safe and appropriate, sessions with a coparent may improve engagement and treatment success for fathers receiving F4C, while substance misuse by fathers may hinder treatment outcomes.</p>