The aim of this study was to investigate second-grade elementary school students' performance related to their counting skills, place value understanding, and addition operation in natural numbers. A total of 205 second-grade elementary school students from Turkey participated in this study. The data were collected through a 'Personal Information Form,' 'Counting Skills Test (CST),' 'Place Value Understanding Test (PVUT),' and 'Addition Operations Test (AOT).' The data were analyzed using independent samples t-test, correlation coefficient, and regression analysis. It was indicated through the results that the second-grade students demonstrated their highest performance in counting skills and lowest performance in understanding the concept of place value. No significant difference was determined between the female and male students' performance as it related to CST, PVUT, and AOT. There were moderate positive relationships between the students' performance related to counting skills, place value understanding, and addition operation in natural numbers. It was also shown in the results of the regression analyses that the addition operation, place value understanding, and counting skills performance in natural numbers were all important variables predicting students' mathematics achievement and explained 61% of the total variance.