This project investigated the quality of the planetarium as a teaching device by contrasting the performance of students taught in the planetarium with the performance of those taught in regular classrooms. Data for the study derived from official records of Cerritos and El Camino community college students enrolled in introductory astronomy for spring 1975. Performance assessment involved comparing three planetarium and non-planetarium student sub-groups: (1) by high, medium, or low academic ability as indicated by mean community college grade point average (3.0 or higher, 2.0-2.9, and less than 2.0); (2) by sex; and (3) by age. Performance criteria included grades on homework, unit tests, mid-term tests, and final course grades. Of the 135 planetarium students, 28% received grades of A, 40% grades of B, 15% grades of C, and 15% grades less than C. Of the 106 non-planetarium students, 11.3% had grades of A, 30% grades of B, 25% grades of C, and 34% grades less than C. Planetarium instruction was positively significant for low, medium, and high ability students, for both males and females, and for all age groups examined (under 30, 30-39, and 40 or over). Data tables and a bibliography are included. (TR)