Assessed was the science achievement of five-and six-year-olds from different socioeconomic backgrounds. Classes included both a middle-class and lower-class pre-school class and a middle-class and a lower-class first grade class. Four additional classes, which were studying a local science curriculum, were chosen to match these same grade-level and socioeconomic criteria. Instruction was given in the experimental and control classes from September, 1966, through May, 1967. Achievement was assessed by administering competency measures to five randomly selected students from each class after the completion of each of eight exercises. Students in the experimental group scored higher than students in the control group indicating that the impact of a curriculum structure is measurable. Five-year-olds scored as well as six-year-olds indicating that age was not a factor in science achievement with this sample. When evidence of science achievement required verbalization, middle-class students did better than lower-class children. When non-verbal behaviors were required no achievement differences were recognized. (BC)