The problem in this experiment was the determination of the value of the part-method in the acquisition of motor-habits when the unit-reactions are functioning parts of the complete process ultimately developed. Ninety undergraduate students of education acted as subjects for the tests. The task consisted in striking one series of numbers with the left hand on one typewriter and another series of numbers at the same time with the right hand on another typewriter. One group of subjects learned the task by first practicing the hands separately; the other group used both hands from the start. An examination of the results tabulated in terms of total time, total errors, and total number of trials, indicates clearly that under the conditions of the experiment the part-method of learning is more economical than the whole method. The scores for time, errors, and trials are consistently smaller for those individuals who established the motor-habit by first using the hands separately. From Psych Bulletin 21:05:00444. (PsycINFO Database Record (c) 2006 APA, all rights reserved)