Background. The paper describes the results of the experimental study of working memory in early schoolchildren and adolescents. The capacity of working memory develops through preadolescence to adolescence, while the developmental changes of representations of serial order are not clear enough so far.

Objective. The accuracy of delayed reproduction of movements (the open polygonal chains, trajectories) reveals. The sample included 32 early schoolchildren (mean age 10.4±0.75 years old) and 25 adolescents (mean age 14.6±0.3 years old). The subjects reproduced trajectories of different length (from 4 to 6 elements) using the graphical tablet. Another factor in the experiment carried out was a mode of stimulus presentation: the trajectories in were presented either as a static line-drawing (static mode) or a small moving pointer (dynamic mode).

Design. The errors of reproduction in two age groups and in different conditions were analyzed. We distinguished three types of errors: (1) severe distortions which are caused by inability to keep the sequence in working memory; (2) insertions or omissions of elements of the trajectory which are related to the problems of encoding the visual spatial information in the motor representation; (3) distortions of proportions of the trajectories, which are related with visual-motor coordination during motor reproduction of the sequences.

Research results showed that in adolescence the accuracy of delayed reproduction is better than in early ages. The most obvious difference in accuracy between the groups of early schoolchildren and adolescents were observed in dynamic mode. The analysis of different types of errors revealed that adolescents less often make insertions and omissions of elements. It may be caused by development of executive functions in adolescents.

Conclusion. The study showed that the capacity of working memory increases in adolescents. In addition, the precision of the representation of serial information are higher in adolescents in the more complicated dynamic mode.