The aim of this study was to investigate the specific numerical and calculation abilities of 28 children with ADHD without comorbid mathematical learning disabilities (LD), ranging from the 1st to the 5th grade of primary school, and to examine the stability or the development of the arithmetic profile. Our results showed that a high percentage of children with ADHD have severe difficulties on numerical and calculation tasks, particularly with counting and arithmetical facts, and these percentages increase with age. Whereas younger children show more problems with lexical processes, for older children, mental calculation and counting processes are particularly difficult. The older students had a statistically worse performance than the younger students on the two measures of time (i.e., mental calculation time and counting time), indicating automatization deficits. This study underlines the importance for teachers to taking the individual arithmetic profiles of children with ADHD into account and of identifying the processes which should be enhanced through education and teaching interventions.