The aim was to study effects of an extension of physical education and motor training on motor skills, attention and cognition during a period of three years. The study has two intervention groups (n = 152) that have physical activity and motor training one lesson every school day and one control group (n = 99) that has the school's ordinary physical education two lessons per week. The method is hypothetic-deductive. The results confirm the hypothesis that children's motor skills improve with extended physical activity and motor training. The hypothesis that children's attention will improve cannot be confirmed. Although pupils in intervention groups have better attention in school year 2 than pupils in the control group, the differences do not remain in school year 3. The third hypothesis concerning academic achievements is confirmed by several results in Swedish and mathematics. The MUGI observation programme was found to be useful both as a screening and as a pedagogic instrument. (Contains 1 table and 1 figure.)