This study reports on a research and development project in a Swedish primary school with seven self-contained classes for pupils with developmental disabilities (Compulsory school for students with intellectual disabilities). In the recent decades there has been an overall movement towards more collaborative forms of developing the pedagogical practice in Swedish schools and this project draws on collaboration between the professionals in the school (special teachers and paraprofessionals), the municipality and researchers from two universities (Kristianstad university and Malmö University). The aim with the project was to contribute to the teachers and the paraprofessional’s professional development within in the field of assessment forlearning (AfL) with the purpose to improve the students achievements. Research by Black & Wiliam (1998) and Hattie (2008) has shown that assessment for learning (AfL)/formative assessment is a powerful tool to improve students’ achievements, but there is not much research conducted in this field in relation to students with developmental disabilities. This research and development project can hopefully contribute with new knowledge in this field. The data material is drawn from observations, interviews, group discussions and documents produced in the project and were collected in a Swedish primary school over a period of 12months.. Analytically, the paper is inspired by Biestas (2010) ideas of education and the model in which Biesta refers to three functions of education: (1) qualification, which involves providing participants with the knowledge, (2) socialization, which is concerned with integrating individuals into existing social, cultural and political orders through the transmission of norms and values; and (3) subjectivation, which concerns the process of individuation, or becoming a free subject of action, responsibility and independence. Preliminary results indicate that both teachers and paraprofessionals has developed their educational philosophy and has developed the ability to give students feedback that the helps the students to improve their learning. From a student perspective, the students has, through the professionals' changed way of giving feedback and informing the students about their achievements, become more engaged and involved in their own learning and have become more aware of the educational goals they are working towards and also more aware of the strategies about “how to get there”. The project has also been working for peer feedback developed with the support of the use of Ipads and smartboard as tools to give the student opportunities to reflect on their own and their peers' learning by watching videotaped lessons.