Knowledge growth models based on first principles play a fundamental role in cognitive sciences. Authors submit an extension of the ENKI (Efficacy Norm of Knowledge Increase) model from 2005 together with actual test results. Tests were administered by the method developed for the purpose of model ENKI, which involves problem solution with immediate feedback. ENKI was applied to the topic of parallel and serial configuration of resistors in electrical circuits, and 74 pupils of six elementary schools took the test. We found that 37% of pupils have mastered the subject, 13% of pupils showed no improvement, while 50% of pupils showed increased proficiency in accordance with the ENKI model (at significance level Alpha=0,05). After attempting solution of six typical problems with immediate feedback, 90% of pupils achieved mastery of the given subject.