Multi-tiered behavioral classroom interventions are particularly important for students with or at risk for ADHD or other externalizing behaviors. Teachers often use these interventions infrequently or not as designed, and little is known about the barriers and facilitators to their use, especially from the teachers’ perspective. Using an exploratory sequential approach, we first used semi-structured qualitative interviews to identify teacher-reported barriers and facilitators to using three Tier 1 and one Tier 2 behavioral classroom interventions with students with ADHD symptoms (Study 1). Then, we identified which barriers and facilitators were most frequently endorsed on a survey (Study 2). The types of barriers and facilitators that emerged from semi-structured interviews included teachers’ beliefs about behavioral classroom interventions (i.e., about their effectiveness or the consequences of using them) that motivated teachers or reduced their motivation to use them, as well as factors that interfered or assisted with execution in the moment. The most frequently endorsed barriers were being distracted or forgetting due to competing demands, and feeling “stressed, frustrated, or burned out;” frequently endorsed facilitators included having a strong student–teacher relationship and having built the habit of using the intervention. Together, these results identify specific, malleable factors that can be targeted when supporting teachers in using Tier 1 and Tier 2 behavioral classroom interventions for students with ADHD symptoms.