A descriptive study was conducted to assess the knowledge regarding childhood Attention Deficit Hyperactivity Disorder (ADHD) among school teachers in selected schools at Kollam district. A non-experimental descriptive research design was adopted, and a purposive sampling technique was used to select a sample of 100 school teachers working in lower and upper primary schools who fulfilled the inclusion criteria. Data were collected using a socio-demographic proforma and a structured knowledge questionnaire consisting of 25 multiple choice questions. The results showed that 4% of the teachers had very good knowledge, 21% had good knowledge, 36% had average knowledge, and 39% had poor knowledge regarding childhood ADHD, with a mean knowledge score of 12.45 (SD = 4.31). Chi-square analysis revealed a significant association between knowledge and medium of instruction (χ2 = 10.730, df = 3, p = 0.013), while no significant association was found between knowledge and other socio-demographic variables such as age, gender, teaching experience, type of school, educational qualification, subject taught, and class teacher status. The study concluded that a considerable proportion of school teachers had inadequate knowledge regarding childhood ADHD, highlighting the need for structured training and awareness programs to strengthen teachers’ ability to identify and support children with ADHD.