Attention-deficit/hyperactivity disorder (ADHD) has a significant impact on children's social, emotional, and academic performance in school, and as such, teachers are in a good position to provide evidence-based interventions to help ensure optimal adjustment of their students. The current study examined teachers' knowledge and beliefs about ADHD, their self-reported use of evidence-based instructional and behaviour management strategies in the classroom, and the relationships between knowledge, beliefs, and classroom practices. It was expected that teachers would have a moderate amount of knowledge about ADHD, mixed positive and negative beliefs about ADHD, that they would regularly use less intensive evidence-based behaviour management strategies, and that more knowledge and positive beliefs about ADHD would be correlated with higher use of effective classroom practices. Web-based questionnaires were completed by 113 teachers from six school boards across Nova Scotia. Results indicated that the mean teacher knowledge score was ~68% and that they had more knowledge about symptoms/diagnosis of ADHD and less knowledge about general ADHD facts and about evidence-based treatments. Teachers had slightly more positive than negative beliefs about ADHD and reported occasional use of evidence-based instructional and behaviour management practices in their classrooms. There was a significant correlation between teachers' beliefs about ADHD and their use of evidence-based behaviour management practices, but there was no significant correlation between specific ADHD knowledge and classroom practices. Information gained from this study has implications for the content of ADHD teacher training and professional development programs as well as for school psychologists and those in teacher consultation roles.