Professional development of future teachers is based on connecting theory and practice with the aim of supporting and developing critical, independent, responsible decision-making and active teaching. With this aim we designed a blended learning environment with an asynchronous online discussion, enabling collaboration and reflection even when face-to-face communication was not possible. This paper discusses the constructs of social and cognitive components, reflection and collaborative learning in blended learning environments. It presents the results of a study that was conducted on a sample of pre-service primary school teachers studying at the largest faculty of education in Slovenia. The purpose of the study was to determine the intensity, level and content of students' posts in the online discussion, how students assess its usefulness, and whether there are differences in the assessment of goals achieved in teaching practice between the students who were included in the online discussion and those who were not. We found that in the sub-groups where communication between students participating in the online discussion did not develop at the level of interpersonal relations, it also failed to develop at the level of learning. We also found that the online discussion helped the participating students to plan their lessons. In assessing the achieved practical teaching goals, it became obvious that the online discussion had a positive impact on students' perception about adapting their lessons, as well as on their critical assessment in analysing their teaching.