This quantitative study examined the knowledge levels middle school teachers in South Texas have in relation to attention deficit hyperactivity disorder (ADHD). The study specifically compared teacher knowledge levels among three specific ADHD knowledge areas: (a) general knowledge of ADHD, (b) knowledge of symptoms/diagnosis of ADHD, and (c) knowledge of treatments for ADHD. The three subscales were measured by the study instrument, Knowledge of Attention Deficit Disorders Scale (KADDS). The sample for this study involved 107 teachers from five predominately Hispanic middle schools in South Texas. The middle schools were in three independent school districts, and data were collected during the 2008–2009 school year. Results indicated that teachers’ greatest area of knowledge dealt with identifying the symptoms/diagnosis of ADHD. Teachers had lower scores related to general knowledge and knowledge of treatments for the disorder. Implications of the study results are discussed, and recommendations are presented.