This paper reports the interim results of a quasi-experimental evaluation of the Chicago Mastery Learning Reading Program, an application of Bloom's mastery-learning instructional model to the elementary reading curriculum. Two approximately equivalent classrooms were selected from each of 10 inner-city schools with minority pupils who were below grade level in reading. In some cases, classrooms were randomly assigned to treatment; in the others, teachers and principals made the assignment. The reading comprehension subtest of the Iowa Tests of Basic Skills was used as a pretest and was repeated in January using a different form. Although the control group scored significantly higher on the pretest, a variety of analyses indicated greater gains for the experimental groups. Spring results are expected to confirm the superiority of the experimental program. (Author/AA)