Students with attention-deficit/hyperactivity disorder (ADHD) often experience school-related difficulties. Although evidence-based classroom management strategies (CMS) are known to alleviate such problems, they are rarely implemented. The current study examined whether a path model including variables influencing the use of effective CMS developed by top-down methods can be replicated utilizing an open science method. An extended model including class size and experience with children with ADHD was also calculated. We further explored prominent implementation barriers. N = 336 in-service teachers completed an online survey. Perceived effectiveness, training on ADHD, perceived disruption, and affiliation with primary/special educational needs schools were important variables associated with the use of CMS. While class size was not correlated with the use of CMS, experience mediated by training revealed an indirect association with it. Class size, lack of time, and many students with disabilities were the most frequently reported implementation barriers. The implementation of effective CMS could thus be mainly enhanced by improving how effectiveness is perceived and by engaging teachers in ADHD-specialized training. Preparing teachers in how to cope with potential barriers should also be considered.