Concern about the quality of science teaching has reached the centre of discussion in Portugal, driven largely by an international survey which pointed to the low achievement of Portuguese pupils (OECD/PISA, 2005). The ensuing national debate culminated in a reform of science teaching for Middle School which focused on new orientations for teaching and learning sciences (Galvão et al., 2002). The new curriculum has a constructivist focus, values the scientific inquiry approach and the formative assessment, and promotes the Science-Technology-Society-Environment (STSE) perspective. The new curriculum in Portugal for science teaching in middle school pushes the teachers towards new teaching approaches. There is a need to explore various approaches to help teachers develop a disposition to implement, reflect and retry new teaching approaches and become involved in a process of practical research (Sagor, 2005). This study reports to the changes occurring in 8th grade pupils' perceptions in relation to assessment process when they're involved in inquiry activities. It is part of an extended study that involved schoolteachers implementing inquiry activities. The research reported in this study is qualitative, adopting an interpretative orientation. A constructivist view of learning supports this investigation and considers that knowledge is constructed by individuals based on their interpretations of experiences. Thirty-nine pupils, attending two 8th grade classes in middle school, participated in this study. The school belonged to a rural area of the country. The data sources used were the interactions among pupils during the lessons, focus group interview, at the end of the study, and written documents produced by the participants (Patton, 1990). The data analysis was inductive, consistent with a naturalistic research paradigm, and consisted of examining the data uncovering salient patterns, singularities, and themes associated with research question. The study showed that, during inquiry activities, formative assessment, as Black (1998) suggest, can be developed in science class, with an increase in participants' interests and motivation. Before the study, pupils felt that were assessed by what they had to memorize. After this study, almost all the pupils argued that this assessment process was a proper way to assess their learning and that they had the opportunity to "discover" contents, instead of memorizing and reproducing it in the exams. During the teaching of Sound through investigations (Wellington, 2002), self-assessment was used to help pupils reflect upon their own thinking. They spend a great deal of time collaborating with others to reach a consensus, and they learn from one another, as they learn content in a positive environment that values all learners' opinions. While performing the inquiry activities, pupils are developing knowledge competences related with sound and also reasoning, procedural, communicative and attitudinal competences as the National Curriculum recommends.Black, P. (1998). Testing: Friend or foe? Theory and practice of assessment and testing. London: RoutledgeFalmer Galvão, C. (Coord.), Neves, A., Freire, A. M., Lopes, A. M., Santos, M. C., Vilela, M. C., Oliveira, M. T. & Pereira, M. (2002). Ciências Físicas e Naturais. Orientações Curriculares para o 3º ciclo do ensino básico. Lisboa: Ministério da Educação, Departamento da Educação BásicaOECD (Organization for Economic Co-operation and Development) (2005). Assessment of scientific literacy in OECD/PISA project. http://www.pisa.oecd.org/ Patton, M. Q. (1990). Qualitative evaluation and research methods (2ª ed.). Newbury Park, CA: Sage Publications Sagor, R. (2005). The action research guidebook. Thousand Oaks, CA: Corwin Press Wellington (2002). Secondary Science - contemporary issues and practical approaches. London: RoutledgeEuropean journal