This study investigated factors associated with top and bottom achievement groups for students enrolled in the Intermediate Science Curriculum Study (ISCS) program. Differences between achievement groups within Levels I, II and III of ISCS were also investigated. A cross-sectional sample of Level I (n=372), Level II (n=290) and Level III (n=379) served as the data source. Students were enrolled in one of two junior high schools within the suburban Philadelphia school district. Achievement was treated as a dependent variable. Achievement groups were contrasted on a series of eleven factors with their counterparts within and between levels using discriminate analysis. Significant differences were found between achievement groups at all levels. Working style and emotional attitude toward science were sharp points of contrast between high and low achievers. Comparison of low achievement groups between Levels I and II, and II and III indicated that reading was the only factor which differed significantly. Similar comparison with high achievers indicated an increased need for computational skills and mathematical apptitude in proceeding from Level I to II. (Author/HM)