Although an average of one to two children per classroom suffer from ADHD, empirically supported classroom interventions are not yet implemented possibly because of teachers' lack of knowledge or negative attitude towards them. To investigate this science-practitioner gap, we need an instrument assessing knowledge, attitude and the use of ADHD-related interventions. The self-report ADHD Questionnaire by Kos and the ADHD specific knowledge and attitudes scale for teachers by Mulholland et al. are examples of such instruments . Yet, these instruments have primary weaknesses concerning their content validity. Our study validated a newly developed instrument. The ADHD-school-expectation questionnaire (ASE) consists of an ADHD knowledge (24 items), attitude (33 items), and intervention scale (27 items). Attitudes are formed by expectations and related ratings according to Fishbein's and Ajzen's rational choice theory and Ajzen's theory of planned behaviour. Our study results revealed theory-based content validity and good reliability. Therefore, the ASE can be used for future research in the field of ADHD in the classroom.