This report presents the results of a teaching experiment which investigated (1) the role of mathematical experiences on the development of counting, addition, subtraction, mental arithmetic, classification, and other arithmetical topics and (2) the role of quantitative comparisons and class inclusion as readiness variables for learning the content in (1). The readiness and achievement variables are discussed in detail and tasks are described carefully. Forty-eight first graders were tested and interviewed, with each of the three interviews videotaped. Data were extracted from the tapes and coded. Twenty-four pupils were given instruction on the concepts for 12 weeks. Multivariate analysis of variance, univariate analysis of variance and discriminant functions as necessary, and correlation matrices were used. Results are presented and discussed in detail. (MS)