Reported are the results of a study to determine if specific errors in subtraction occur when students demonstrate ability to apply selected decimal numeration system principles. A secondary purpose was to examine and compare errors made by various subsets of the sample population characterized by grade level, arithmetic achievement, mental maturity, and mean achievement level of the school attended. Knowledge of place value and subtraction skills were measured by another-designed instruments. A positive correlation (.68) existed between performance on place value and subtraction tests. In general, high achievers and high mental maturity groups made significantly fewer (.05) errors than the corresponding low groups. Low achievers generally were unable to apply decimal numeration principles. (Author/RS)