This study investigates the knowledge and attitudes toward Attention-deficit/hyperactivity disorder (ADHD) among a large cohort of mainstream and special education in-service teachers in Israel. Given the pivotal role of teachers in identifying and managing ADHD symptoms within the classroom, it is crucial to ensure they possess adequate knowledge and positive attitudes toward the disorder. Previous studies have indicated a gap in knowledge and attitudes between mainstream and special education teachers, often influenced by factors such as teacher training, personal experience, and demographic characteristics. This study addresses these gaps by utilizing the well-validated ASKAT questionnaire to provide a comprehensive assessment of teachers' knowledge and attitudes toward ADHD. A total of 538 teachers participated, including 288 mainstream and 250 special education teachers. Results indicated that special education teachers demonstrated higher levels of knowledge and more positive attitudes toward ADHD compared to their mainstream counterparts. A significant positive correlation was found between knowledge and attitudes among mainstream teachers, but not among special education teachers. Additionally, demographic factors such as gender, age, and current teaching experience with ADHD students were significant predictors of teachers' knowledge and attitudes. The findings highlight the need for targeted professional development programs to enhance ADHD-related knowledge and attitudes, particularly for mainstream teachers. By identifying specific areas where mainstream teachers may lack knowledge or hold less positive attitudes, this research can inform the design of effective interventions. Ultimately, this study underscores the importance of ongoing teacher training to foster more inclusive and supportive educational environments for students with ADHD.