The present invention relates to a computer training system for training working memory capacity of a user of a computer within the system, and a computer program to be used within said system, a first task of a first difficulty level is presented to the user, a delay of a predetermined time is performed, during which delay the task is not visible or audible to the user, and during which delay it is not possible to enter an answer into the computer, the difficulty level of a subsequent task to be presented to the user is changed in accordance with predetermined adaptation rules and based on said evaluation such that the difficulty level of the subsequent task is adapted to the capacity of the user, subsequent tasks are presented to the user adapted to the capacity of the user in until a predetermined time limit is exceeded or until a predetermined number of tasks has been performed.