Musical aptitudes must be apparent in children who are going to participate in musical groups during their free time in institutions for resocialization. Such aptitudes include an 'ear' for music--i.e., a skill for recognizing melodies or being able to recall melodies or fragments off melodies--and a sense of rhythm and timing. Standard musical aptitude tests can be used to discover these skills. The workroom for such a project should have, ideally, many different kinds of instruments--recorder, a small library of music, portraits of well-known Polich and foreign composers, and blackboard. The room should be conducive to persons meeting to play music together and the are in each other's musical achievements. What such musical exercise can do is awaken interests in students. reveal their own capilities and instruct them in performing together. Music groups a s such can work with singing songs, playing instruments, listening to music, dancing the rhythm, and composing music. An experiment conducted with girls at a resocialization school for delinquents concentrated on singing and listening. The singing aimed to bring out the joy of making music with one's own voice and to train the girls to work together. Listening to music was designed to damiliarize the students with various kinds of music, both classical and popular, with the composers' lives and ideals, and with thematic and theoretical aspect of music. Field trips were organized to take the students of music programs so they could hear fine music first-hand. Of the 70 girls, 66 were highly appreciative of the role of music in human life, 3 were indifferent, and 1 was openly opposed to music as a bad influence on people. The music group enhanced the girls' individuality, their sensitivity, their creativity, their patience, their abilities to work in a group, and their sense of morality and society. Most important was that they enjoyed it, especially as popular music was studied along with classical music. --in French.