The article investigates the interplay between the meaning given to certain key expressions and pupils' understanding of science subject matter, in a qualitative study of learning.The intentional-expressive approach to the epistemological role of language use served as a theoretical frame, within the wider context of phenomenographic research on learning. Data were collected using a particular dialogue structure. Micro-process analysis was employed to examine the data. Two descriptive categories emerged: 1) "Exploring the function of meaning", and 2) "Inventory of meaning". Pupils who explored the function of meaning related their explanations, both to other expressions, and to their personal understanding of the physical problem. Pupils who made inventories of meaning mostly directed attention towards expressions as words. Emphasis was on correct reproduction of scientific terminology. Inventory of meaning was most common in the dialogues with the fourteen-year-olds, while exploring the function of meaning dominated in dialogues with the ten-year-olds. (Contains 3 figures and 1 table.)