School-based health activities that involve parents are more likely to be effective for child health and well-being than activities without a parent component. However, such school-based interventions tend to recruit the most motivated parents, and limited evidence exists surrounding the involvement of hard-to-reach parents with low socioeconomic status (SES). Mothers remain responsible for the majority of family care; therefore, this study investigated mothers with low SES to establish the reasons and barriers to their involvement in school-based health activities and to propose strategies to increase their involvement in those activities. Interviews were conducted with mothers with low SES, who were typically not involved in school-based health activities (n = 16). An inductive-deductive approach to hierarchical analysis revealed that there are several barriers resulting in mothers being less involved, particularly due to issues surrounding the schools' Parent Councils and the exclusivity of school-based events. Efforts made by the school to promote health activities and involve parents in such activities were revealed, alongside recommendations to improve on these practices. The findings offer multiple ways in which future school-based health interventions can recruit and involve mothers with low SES.