This study was an attempt to determine the relationship between students' performance on an achievement test for a given unit in the Introductory Physical Science (IPS) curriculum program and the time spent teaching the unit. The sample consisted of 974 eighth- and ninth-grade students and five IPS teachers. The SCAT Test and the Standord Achievement Test were used as instruments, as well as the IPS Achievement Test for a particular unit. The SCAT-score-to-IPS-score conversion tables and a regression equation were used to predict an expected score on the IPS Test. Scatter diagrams were constructed to establish the relationship between variables. Correlation coefficients were calculated to determine if significant relationships existed between: (1) teaching duration and mean adjusted achievement gains, (2) teaching duration and mean past science achievement gains, and (3) teaching duration and aptitude. Significant differences were found between the latter two stated variables and teaching duration. The classes with the highest mean past achievement required less teaching time; classes with the highest mean aptitude also required less teaching time. (Author/EB)