A study investigated the effect of kindergarten class size on reading readiness achievement. Subjects, 2,837 kindergarten students in 38 elementary schools that serve rural, urban, suburban, and inner-city schools, participated in the first year of Project STAR (Student Teacher Academic Ratio) in 1985-86. The subjects' 140 kindergarten teachers reported data indicating mastery or non-mastery of the 25 reading readiness objectives of the Tennessee Basic Skills First program. Data were analyzed using a five-way analysis of variance and a crosstabulation procedure with a chi-square test of significance. Results indicated that: (1) small class size is significantly related to reading achievement in the total 25 tested Basic Skills and the subcategory of 20 comprehension skills; (2) the 1:15 class mastered one more objective than the 1:25 class and 0.6 more of an objective than the 1:25 plus a full-time aide class; (3) no significant relationship was found between classes of 1:15, 1:25, or 1:25 plus a full-time aide and the mastery of the five word identification skills; (4) the 1:25 class was found to be least effective in achieving reading readiness; (5) students in classes of 1:15 who attended 90 percent of the time showed the greatest gain; and (6) the lowest mean scores were received by males, blacks, free/reduced lunch, and inner city students in the 1:25 class, and the highest scores for this group were in the 1:15 class. Recommendations include mandatory kindergarten with a teacher/pupil ration of 1:15. (Twenty-three tables and 58 figures of data are included; 95 references, House Bill No. 544, the Tested Basic Skills Individual and Group Records, and 25 tables of data are attached.) (RS)