Sažetak Counting is a skill which is mastered by children relatively early. In this process they have to adopt some basic principles (one-to-one correspondence, stable order principle and cardinal principle). Notwithstanding the numerous studies, there is still a strong debate on whether the adoption of principles in counting comes before the skill, or the sequence of adoption is reversed. In accordance with the "principles before skill" model, this study examined whether there are differences in the counting performance of children of different ages,k with regard to the arrangement of elements in the set; whether there are difference3s by age in children's performance in the recognition of correct and incorrect counting performed by somebody else (a puppet) and whether there are differences in children's performance in counting (procedural knowledge) and recognition of correctness of counting (conceptual knowledge). A total of 88 participants took part in the study. They were divided into three age groups: younger (from 5 to 6), medium (from 6 to 7) and older (from 7 to 8). It was established that children from the medium and older groups are significantly more successful in counting that those in the younger group. The participants were most successful in counting on the set with elements arranged in a row, followed by a triangle and they were least successful when the elements were arranged in a circle or randomly. The puppet's correct and incorrect counting is recognized equally well, where the children from the older and medium age group are again more successful than the children from the younger group. Children's performance in counting is significantly better than their performance in the recognition of counting correctness. The findings did not confirm the "principles before skill" model. On the contrary, they suggest better children's adoption of procedural rather than conceptual knowledge.