A study of 180 seventh grade students was conducted to discover the relative value of teaching vocabulary by teaching whole words contrasted with teaching prefixes. Two experimental groups and a control group were formed of equal numbers of high, middle, and low ability students based on their scores on the Nelson Reading Test. One experimental group was taught prefixes, whole words, and their meanings. The other experimental group was taught only whole words and their meanings. The control group did free reading during the instruction time of the experimental groups. Each group was given a pretest, a posttest, and a delayed posttest. Both experimental groups did better on the posttest and the delayed posttest than did the control group. The prefix treatment, which took no longer to administer than the whole word treatment, resulted in students learning more prefixes and in their being able to use their knowledge of the prefixes to unlock the meaning of novel words. (TJ)