The present paper aims to explore how a certain class mode emerges in the context of collaborative learning, which affects student motivation and learning. Multiple sources of data were collected from 51 high school students in three different classes (named A, B and C) where the same teacher gave them the same lesson content throughout a full year. A quantitative analysis of multiple questionnaire responses revealed that patterns of motivational change and change in perception of pair and group work were markedly different in the three classrooms. A qualitative data analysis of interviews and observations of pair and group activities showed that different classroom modes of regulation are likely to emerge even among homogenous classes consisting of students with the same L1 and similar proficiency levels under the same curriculum. The findings imply that socially-shared regulation among students is one of the keys to creating a positive classroom environment in which students influence and motivate each other.