Among all the goals and tasks that the assessment process involves in education, it mainly concerns collecting and reviewing evidences in order to be able to evaluate learner learning and performance. Therefore, assessment is definitely an integral part of the learning process. In addition, there is evidence that the perception that students have of the assessment influences how they learn and work. Unfortunately, in practice, from the point of view of learners, the assessment process is most of the time highly disconnected from the flow of learning activities and it is organized as a black box in which they are usually very less involved. One way to integrate assessment in the learning process is to shift from assessment of learning, the summative side of assessment, which remains most of the time the main focus, to assessment for learning, the formative side of assessment. However, even if it is discussed and challenged, assessment of learning remains necessary in most of educational contexts and can not be simply abandoned. Therefore it is necessary to define assessment approaches that can embed both aspects. Peer assessment seems by nature a good candidate approach to involve learners in the assessment process and integrate assessment in the flow of learning activities. Peer assessment has recently received an increase of interest with the advent of Massive Open Online Courses (MOOCs): peer assessment allows outsourcing the assessment of learners' work that would otherwise be difficult to achieve for very huge class size. In this paper we first describe a social learning online environment where learning activities are mainly organized around the concept of group. The purpose is to provide an open learning context to develop teaching activities that combine formal and informal learning. Each group has a virtual space in which peers can collaborate using a toolbox. It supports peer learning through different interaction mechanisms for peer feedback and peer assessment. We particularly focus on the design and implementation of a workflow for inter-group peer assessment of group work. It relies on a simplified portfolio approach and the related components and widgets are integrated inside the group space in order to integrate the peer assessment into the group learning activities. We then describe how the proposed peer assessment framework has been used to support the semester project of a first year bachelor course and the global organization and setup of this semester project. This is an introductory course in information systems intended mainly for management students. For this experiment, the class size about 250 students. The course includes a semester project where students are organized in groups of four. The group work is supported by the online environment. Each group has its own space and is free to use the available toolbox to communicate, exchange, collaborate and produce their outputs and submit their deliverables. The project is organized into successive steps planned along the semester. Guidelines are provided either during face-to-face session or through the online platform. Inter-group peer assessment is included as one of the step of the semester project. We finally discuss and analyse the results of the experiment. We particularly target two quantitative indicators. The first one is the confidence of peers regarding their evaluation: do they trust the result of their evaluation? The second is the impact of the peer evaluation process regarding their own work: would they correct their own project after evaluating their peers' one or not? Both indicators provide a possible framework to evaluate the relevance of peer evaluation and the confidence that can be granted to it from the point of view of the learners. We also compare tutors' evaluations with peer evaluations and describe how this formative assessment schema can be used to support summative assessment.