Most parenting interventions report high dropout rates for parents who exhibit clinically high levels of stress and/or are parents of adolescents with severe emotional and/or behavioral difficulties. The objective of this preliminary study was to evaluate the feasibility and real-world effectiveness of the Open Door Approach to Parenting Teenagers (APT), a six-session individually delivered face-to-face intervention for typically hard to engage parents of 11 to 21-year-olds. A one-group, pre-post evaluation design was adopted due to the naturalistic clinic-based setting of the study. Participants were 279 parents reporting clinical levels of stress relating to parenting an adolescent. Parents receiving the APT intervention demonstrated lower dropout rates than other parenting programs and reported high scores across several items relating to service satisfaction. The APT intervention was associated with significant reductions in parental stress and improvements in parent-adolescent relationships immediately post-intervention. Findings suggest that parents found the APT intervention acceptable and beneficial, and further suggest that the intervention is feasible and effective in retaining hard to engage parents. Moreover, preliminary findings suggest that the APT intervention is a promising intervention that may support parents who fail to engage in group programs. However, further research is required to establish the efficacy of the intervention.