This study examined whether the educational practice of retaining students in junior first grade for a year between kindergarten and first grade enhanced their academic achievement and self-concept of academic ability. Subjects were 120 students randomly selected from a midwestern school district and divided equally into 4 groups: (1) recommended for first grade and placed in first grade; (2) recommended for junior first grade and placed in junior first; (3) recommended for junior first grade but placed in first grade; and (4) borderline between junior first grade and kindergarten, but placed in first grade. The groups were compared on 14 variables: (1) gender; (2) birth month; (3) retention; (4) absences; (5) lunch status; (6) class placement in mathematics; (7) grade point average in mathematics; (8) mathematics total on California Achievement Tests; (9) category of achievement in mathematics on the Michigan Educational Assessment Program; (10) class placement in reading; (11) grade point average in reading; (12) reading total on California Achievement Tests; (13) category of achievement in reading on the Michigan Educational Assessment Program; and (14) self-concept of academic ability. Males were retained in junior first grade at twice the number of females, and several variables were significantly different for the four groups, including self- concept of academic ability. Findings indicated that an extra year of junior first grade did not enhance academic achievement or self-concept of academic ability. (Contains a 49-item bibliography.) (WP)