Two experiments tested the applicability to human beings of findings with animals that the number of performances required for the reinforcement of one behavior affects the subsequent effort expended in other instrumental behaviors. In Exp I, 12 adult depressed psychiatric patients worked on a sorting task for the approval of a staff psychologist. The time spent and the work completed were increased by prior approval from a ward attendant for each completion of several custodial tasks, as compared to the attendant's approval for each completion of a single task or a no-pretreatment control condition. In Exp II, 11 preadolescent learning-disabled students who were required to read and spell correctly a greater number of words per reward token later spent more time and completed more work for reward tokens in mathematics and handwriting. Results suggest that individual differences in general persistence may arise, in part, from an accumulation of effort training in the natural environment. (24 ref) (PsycINFO Database Record (c) 2006 APA, all rights reserved). © 1979 American Psychological Association.