Assess (a) the variability of behaviour problems in children with Hyperkinetic Disorder/Attention-DeficitHyperactivity Disorder (HKD/ADHD) across a range of family situations and (b) the degree to which behaviour in each situation can be modified through a cognitive behavioural parent training (CBPT). Furthermore (c), compare the effectiveness of training in two different formats and (d) test the proposition that group treatment benefits behaviour in a wider range of situations than individual treatment. A registered multicentre randomized controlled trial comparing individual and group parent training to treatment-as-usual (TAU) for N=237 children with HKD/ADHD. A German version of the Home Situations Questionnaire (HSQ) was employed to examine behaviour problems across a range of family situations, treatment-related changes post-treatment and at 6-month follow-up, while controlling for medication status. Parents reported considerable variance in severity of behaviour problems across situations. All groups improved with time, but individual and group CBPT led to significantly greater improvement than TAU in many family situations. Results present situation-specific treatment trajectories and demonstrate somewhat greater impact of individual compared with group training in certain situations post-training and 6months later. CBPT clearly adds to TAU (with effect sizes in the small to moderate range depending on situation). Individual was somewhat more successful than group format (which did not succeed in a wider range of situations). HSQ situations reveal a differentiated picture of child behaviour and treatment results. Situation-specific assessment with an instrument like the HSQ offers promising perspectives that invite further development.