: There is a social gradient to the determinants of health; low socioeconomic status (SES) has been linked to reduced educational attainment and employment prospects, which in turn affect physical and mental wellbeing. One goal of preventive interventions, such as parenting programs, is to reduce these health inequalities by supporting families with difficulties that are often patterned by SES. Despite these intentions, a recent individual participant data (IPD) meta-analysis of the Incredible Years (IY) parenting program found no evidence for differential benefit by socioeconomic disadvantage (Gardner et al. in Public Health Resesearch 5, 1–144, 2017). However, it did not examine whether this was influenced by engagement in the intervention. Using intervention arm data from this pooled dataset (13 trials; N = 1078), we examined whether there was an SES gradient to intervention attendance (an indicator of engagement). We ran mixed-effects Poisson regression models to estimate incidence rate ratios (IRRs) for program attendance for each of five (binary) markers of SES: low income; unemployment; low education status; teen parent; and lone parent status. The multilevel structure of the data allowed for comparison of within-trial and between-trial effects, including tests for contextual effects. We found evidence that low SES was associated with reduced attendance at parenting programs—an 8–19% reduction depending on the SES marker. However, there was no evidence that this association is impacted by differences in SES composition between trials or by the attendance levels of higher-SES families. The findings underscore the importance of developing and prioritizing strategies that enable engagement in parenting interventions and encourage program attendance by low-SES families.