The focus of this study is to examine to what extent and in what ways science teachers practice assessment during classroom interactions in everyday activities in an upper-secondary school in Sweden. We are science teachers working now with a larger research project on assessment in science education that seeks to examine teachers' assessment practices in the upper-secondary school. Framing questions include: are teachers performing an integrated assessment of students' skills as the national curriculum mandates? If so, what do the instructional discourses look like in those situations and what are students' experiences regarding their agency on learning and assessment? We emphasize the social, cultural and historic character of assessment and sustain a situated character of learning instead of the notion that learning is "stored inside the head". Teacher led lessons in three science classrooms were video-recorded and analyzed by combining ethnographic and discourse methods of analysis. Both methods are appropriate to the theoretical foundation of our approach on learning and can give some answers to questions about how individuals interact socially, how their experience is passed on to next generations through language and how language use may reveal cultural changes in the studied context. Making the study of action in a classroom the focal point of sociocultural analysis supports the examination of assessment processes and identification of the social roles in which teachers and students are immersed. Such an approach requires observations of how teachers act in authentic teaching situations when they interact with their students in classroom making possible to observe negotiation processes, agencies when both teachers and students are involved in every-day activities. Our study showed that teachers mostly ignored students' questions and that students solved their own problems by helping each other. Teachers did not provide opportunities for students to discuss or argue scientific issues as the national science curriculum stipulates. We found that traditional assessment methods, such as tests, examinations and assignments were the most common methods used to assess and grade students' learning. Different aspects of knowledge stipulated in the national Swedish curriculum, such as lifelong learning, stimulation to students' creativity, curiosity as well as their wish to explore and convert new ideas into action, and find solutions to problems, were restricted by teachers' discourses. The observed teachers' learning and assessment practices constrain students' agency leading to students' silence consequently hindering students' development.