The piece of research work described in this article was concerned with tracing the influence of encouragement given to the pupil at work by commendation and favourable evaluation of his or her work and, on the other hand, the influence of sharp criticism and mistakes being pointed out. On the one hand, we used the method of measuring reaction time to light stimuli, on the other hand the k-test (maze) method. The length of reaction time and the number of mistakes following positive and negative motivation were evaluated with 38 boys and 38 girls taking part. As to the k-test, the time of passage through the maze and the number of errors were evaluated with 20 boys and 20 girls participating and in two more variants of the experiment 59 boys took part. The results have shown that if there is favourable evaluation, there is a quicker attainment and a lower number of errors among boys as well as girls, while unfavourable evaluation leads to lengthening the time taken to respond to the stimulus and increasing the number of errors in case of both boys and girls, and it was so whichever of the two methods was used. The statistical significance of the differences in average time figures as well as in the number of errors following positive and negative evaluation has been proved by either method, but the influence of sex in case of negative evaluation was not statistically proved either in time figures or in the number of errors. The attainment of the pupils is always positively influenced by encouragement in the form of commendation. From the Viewpoint of decreasing the number of errors it doesn’t matter whether the commendation comes before or after the criticism, but from the viewpoint of time figures it does. In order to bring about a positive attitude to work it is appropriate for encouragement to precede critical evaluation.