Background: Attention Deficit/Hyperactivity Disorder (ADHD) is a common psychiatric problem in childhood. For teachers to achieve their roles in early detection and management they need to have good knowledge. Aim of the study: to assess teachers' knowledge and misperceptions about ADHD among primary school students. Subjects and Methods: Research design: A descriptive cross-sectional design was used. Setting: the study was conducted at the primary schools in Abo Hmmad city at El-Sharkia Governorate in Egypt. Subjects: This descriptive cross-sectional study was carried out at primary schools in Abu Hammad city at El-Sharkia Governorate in Egypt on 235 full-time teachers. Tools of data collection: A self-administered questionnaire including the socio-demographic data and Knowledge of Attention Deficit Disorder Scale was used in data collection. Results: Teachers’ age ranged between 25 and 57 years, 74.0% were females and 78.7% from rural areas. Teachers’ satisfactory knowledge was highest for symptoms/signs and diagnosis (52.3%), while treatment was the lowest (30.2%).Overall, 30.6% of the teachers were having satisfactory total knowledge of ADHD .Teachers’ lack of knowledge about treatment was mostly regarding dietary intake of sugar or food additives (51.5%), stimulant drugs (53.6%), and Electroconvulsive Therapy (53.6%). Income and attendance of training courses were positive predictors of most knowledge areas. Conclusion: Primary school teachers have lack of knowledge about ADHD, particularly in the area of ADHD definition, etiology, and treatment. Their knowledge is positively influenced by attendance of training courses. Recommendations: The Ministry of Education should conduct specialized in-service training courses for them to improve their knowledge; the curricula of the Faculties of Education should include related training; the school health team, particularly the nurse, should work closely with teachers for early detection, prompt referral, and proper management of students diagnosed with ADHD.