This paper is based on an interest in increasing the understanding of trends regarding Swedish students ́ knowledge in science by exploring the relation between results of large-scale studies (PISA and TIMSS) and how science teaching and learning are constituted in different school environments. Previous large scale studies point to an explicit downward trend in Swedish students ́ performances in science over the last decade. Our analyses indicate that a reinforced knowledge segregation of Swedish schools and declining results among low- and mid-ranged performers explains a main part of the trend. In this paper we analyze how this trend could be related to and visible in different activities in a science classroom perspective in Sweden today. This means to analyze the use of language and science classroom discourse, in theoretical and practical parts of the classroom activities. In addition, it involves exploring different school areas which have either a large proportions of high achievers or low performers or areas that experienced a substantial improvement or decline during this period. The purpose is to analyze the empirical material which comprises examples of teaching and learning sequences, in a selection of these different schools areas. Our expectations are to increase the understanding of how national trends from large-scale studies are constituted and become explicit, distinguish success and decline factors and identify suggestions of practical action programs for science teaching.