This study examined whether a post-feedback interval varied after an error and correct trials, and determined whether PFI affected subject's performance on concept identification tasks. In experiment I, subjects were given the opportunity to pace themselves, and subjects at Cond. II were also given PFI after responses. On the other hand, subjects at Cond. I were immediately given another stimulus after feedback information. The results obtained were as follows: As the amount of task complexity increased, PFI after an error response lengthened, since more complicated information processing was required after a wrong response. The purpose of experiment II was to examine whether PFI affected children's performance. 88 subjects made of kindergarten children, second and fifth graders, participated in this experiment. Results indicated that most of the fifth graders given PFI achieved a learning criterion, thus reducing errors and trials.