Forty kindergarten children at the Stephen Bull School in Racine, Wisconsin were tested to determine the effects of a sequence of 12 experimental lessons on the ability of kindergarten children to recognize and conserve numerousness. Subjects were 40-low-to-middle socioeconomic level children divided into treatment and control groups. A specially developed test of numerousness (arithmetic readiness) served as a pre- and posttest. The lessons were designed to give experience with one-to-one correspondence and comparisons by counting, relative size and/or relative density. No significant differences were observed between the mean gain scores of the experimental and control groups. However, significant differences were observed between the mean gain scores of children in the treatment groups who attended the half-day session and those attending a special full-day program. A similar result was observed within the control groups. Results indicate that the lessons used in this experiment did not alone sufficiently enhance the subjects' ability to conserve numerousness, but that they should provide an effective supplement to formal activity with number concepts. (Author/WY)