This study was conducted to find out whether extending the kindergarten day with individualized curricula would produce differences in achievement great enough to warrant the increased cost. Two pilot studies were conducted in this large suburban school district, using kindergartens from four of 17 elementary schools. Two of the schools served middle class families; the other two served lower class families and were eligible to receive Title I funds. Educationally advantaged pupils judged 'least ready' on the basis of standardized test results and teacher ratings were selected for inclusion in the extended day kindergarten and control groups. Both extended day groups participated in the regular kindergarten programs in the morning and received an additional 90-minute period of structured activities in the afternoon. These activities differed according to the needs of the pupils and are described in some detail in the report. Results favoring the experimentals over the controls were apparent at the end of the kindergarten year, most noticeably in the educationally disadvantaged sample. (Author/CS)