Ninety-six first grade students in an urban school system were tested in October and May on reading, mathematics, and their understanding of sequences of letters and numbers. A time lag analysis was subsequently conducted. In such analyses, cross-correlation between the first measurement of one variable and the second measurement of another are compared. The larger of the correlations indicates the direction of the relationship; i.e., which variable is most likely to be casual. Correlations of the fall scores on the number sequences with spring scores on the mathematics concepts scale were significant, while correlations of the fall mathematics concepts scores with spring number sequence scores were negligible. This indicates that understanding such complex sequence has a directional effect on understanding mathematics concepts. Fall-spring cross correlations for the letter sequences and reading test, although significant, did not differ, and hence provided no indication of the direction of the relationship. Potential explanations were discussed.