Abstract
Previous research has shown that children with high levels of attention-deficit/hyperactivity disorder (ADHD) symptoms often have a wide variety of associated behaviour problems. However, relatively little is known regarding to what extent these associated behaviour problems are present to the same degree in younger as well as older children and in girls as well as in boys. This study used parent ratings to examine effects of age and gender on behaviour problems, social competence, negative impact on everyday life, and family burden among pre-school and school-aged children high in ADHD symptoms (n=60) and comparison children (n=499). With regard to age, the pre-school children did not differ from the school-aged children on any of the different types of problem behaviour or with regard to social competence. The interactions between age and group were not significant. The behaviour problems of older children did, however, have more negative impact on the child's daily life and induced higher levels of family burden compared with problems of younger children, especially among children with high levels of ADHD symptoms. Boys were more severely affected than girls with regard to ADHD symptom severity, most associated problem behaviours, as well as negative impact and family burden. Significant interactions of ADHD symptoms and gender were also found, which indicated that gender differences were primarily found among children with high levels of ADHD symptoms. Children with high levels of ADHD symptoms have many associated behaviour problems, even in pre-school years, and boys with high levels of ADHD symptoms are more severely affected compared with girls.