An attempt was made to investigate two aspects of the learning and teaching context. One deals with how the sets of beliefs or expectations pupils hold about some phenomena affect the sense they make of experiences given to them in science classes. The other deals with the potential effect of the inevitable use of "scientific" and "everyday" language by both teachers and pupils in instruction. A sample of thirty Portuguese students from grade five to grade nine (10-15 years old) were given laboratory experiences and "parallel" everyday phenomena to discuss individually with the interviewer and then were invited to describe orally what and why things happened. The fundamental conceptions that students hold, the changes of these conceptions with students' age, as well as their consistency in different contexts and in similar tasks were identified in this experiment. The results suggested that these students, although having been exposed to formal teaching, still retain and use intuitive notions to think: about experiences in science lessons. The focus of the second experiment was to investigate how teachers' own perceptions may influence the development of pupils' ideas. It was carried out by observing seven teachers during ordinary classroom activities, to discover the relative contributions of 'scientific' and 'everyday' meaning in the language they used. Common features in teachers' and students' conceptualizations of "heat", "temperature" and "energy" were identified. Two main questions were discussed: i) what are the implications of the semantic variability in the disparate linguistic references for science education? ii) how to bridge the gap between teachers' and students' understandings, i.e., what connections can be made between what teachers and students talk about and perceive from discourse in the classroom? The results of this study seemed to reinforce the idea that it is impossible to keep external, everyday, informal culture out of the science classroom.