Counting abilities have been described as determinative precursors for a good development of later mathematical abilities. However, an important part of variance in mathematical achievement has also been associated with differences between instruction methods given in schools. In this study counting and instruction as predictors for mathematical skills were studied in 423 children. Our data revealed that the mastery of the counting principles in kindergarten was predictive for the risk of mathematical (dis)abilities in grade 1. Moreover, children sharing a common instructional background tended to have more similar scores on mathematical tests, yet, the importance of mastery of the counting principles in the prediction of later mathematical achievement was the same for all classrooms.