Attention-deficit hyperactivity disorder (ADHD) rates in classrooms have increased considerably in recent years. Previous literature has acknowledged the significance of teachers' knowledge and attitudes towards ADHD when making referral and intervention decisions. Using Mulholland, Cumming and Jung's (2015) knowledge (SASK) and attitude (SASA) scales, ADHD training and perceived support were compared across public school teachers (n = 165) and teaching assistants (TAs) (n = 157) in the UK. Results indicated that teachers and TAs displayed adequate levels of knowledge, and TAs held better knowledge and more positive feelings towards ADHD than teachers. Training increased knowledge for TAs, but not for teachers, and training and support appeared important for both the teachers and TAs' attitudes. Both teachers and TAs reported inadequate training and expressed a desire for further ADHD training, and a significant association was found between knowledge and attitudes for teachers only. The implications for these findings are discussed.