The main goal of the research was to study how children develop new competencies within social interaction with more competent peers and adults. The pretestposttest experimental design was used. In the pretest phase 100 Grade 3 students were assessed by the Raven progressive matrices, and based on the results three equal groups for treatment phase were formed (15 students each). In the treatment phase students from the three groups solved 5 items from the zone of proximal development (ZPD) under three different conditions: collaboratively with a more competent peer, collaboratively with an adult, and individually. The post test included assessment by the Raven test after two months. The qualitative analysis showed that all three groups progressed equally, although students who collaborated with an adult were somewhat more successful with items from the ZPD. The qualitative analysis suggested that new competences are developed in different ways depending on with whom student collaborated. The successful peer interaction was marked by higher degree of symmetrical collaboration including higher level of joint critical thinking, and the successful interaction with an adult was marked by higher level of adult guidance as well as more elaborated task analysis, argumentations, and justifications. Based on the results, it is concluded that: (a) children could develop new competences based on both construction and co-construction mechanisms, and (b) the development of new competences through social interaction depends on the partners and the kind of dialog they build during collaboration. .