Existing research suggests that students with ADHD may not receive the expected benefit from some testing accommodations. One possible explanation for this lack of benefit might be that students do not receive adequate instruction in and practice with testing accommodations to make them effective. The current study was designed to investigate teacher belief, knowledge, and practices that may influence the competent use of academic testing accommodations on the part of students. An anonymous survey of current classroom teachers (n = 240) representing the full range of roles and grade spans was conducted via social media platforms. Overall, teachers endorsed beliefs about testing accommodations most positively, followed by practice, then knowledge. Teacher role (i.e., special vs. general education teacher) and grade span taught were associated with beliefs, knowledge, and practice with regard to supporting competent student use of academic testing accommodations. Teacher training was positively associated with teacher knowledge regarding practices that are thought to best prepare students to use their testing accommodations with independence. These findings suggest that additional training may be needed, particularly for certain groups of teachers, in order to promote instructional practices that may improve the successful use of student academic testing accommodations.