Disruptive behavior disorders (DBD) are the most common behavioral health problems in young American children. When not well-managed in early childhood, DBD can progress to lifetime mental health problems with personal, economic, as well as societal impacts. The evidence-based intervention of choice for DBD is outpatient parent-directed behavioral therapy (PDT). However, little is known about clinicians' perspectives on the factors influencing PDT's effectiveness in routine care. The current study directly assesses clinicians' perspectives on factors they believe impact PDT's success for disruptive behavior problems, in particular tantrums, at two outpatient behavioral therapy clinics specializing in PDT. In-depth interviews with 19 clinicians across three experience levels (doctoral intern, post-doctoral, licensed staff psychologist) were conducted and analyzed using qualitative methods. Two major themes were identified as enabling and limiting treatment success: (1) appointment attendance, (2) primary caregiver buy-in to treatment approach. Additional identified factors include caregiver's familial and social support, caregiver's physical and emotional capacities, complexity of the child's behavior problems, the extent to which the home environment can support positive changes, competing family/home demands, and care coordination among hospital programs. The primary factors identified by clinicians highlight the importance of fostering appointment attendance and parental psychoeducation that can be addressed by implementing multi-level administrative, training, and clinical initiatives to improve PDT's real-world effectiveness for DBD.