Classroom settings are pivotal for imparting knowledge. At the same time, this is the place where ADHD symptoms exacerbate (Kofler, Rapport, & Alderson, 2008). The expression of ADHD symptoms seems to reduce appropriate learning opportunities in the classroom and is documented in poorer educational outcomes in children with ADHD (Frazier, Youngstrom, Glutting, & Watkins, 2007). Today, ADHD symptoms are mainly assessed using questionnaires. However, these measures cannot provide ecologically valid information on symptom expression in classroom situations and are furthermore likely to be affected by self-report biases (e.g. recall bias, social desirability). Hence, this study aims at developing a reliable rating system for hyperactivity, impulsivity and inattention. The rating system will be based on filmed behavior in simulated classroom settings of children diagnosed with and without ADHD. The lesson comprises a mathematics test and a competitive card game. Every participant is recorded by a mini-camera, delivering whole-body pictures in a consistent camera perspective. Video material (20 min of each child) will be analyzed by four independent raters with regard to the intensity of hyperactivity, impulsivity, and inattention. (1) We expect a positive association between symptoms assessed via video ratings and questionnaires (self-reported and through parents), and (2) a negative association between the performance in a mathematics test and symptom expression as assessed via video ratings. Groups of five to eight children (9-13 y) with and without ADHD will take part in a simulated classroom lesson. A reliable and economic assessment of ADHD symptoms in classroom settings should enhance ecological validity in the diagnostic process and provide information on the association of ADHD symptom expression and achievement in a math test. Beside this, the study comprises objective movement measurements via Actigraphy and a Five Minute Speech Sample from the parents about their feelings and attitudes towards their child.