This paper draws on the Vygotskian methodological construct of microgenesis to study collaborative activity in an intermediate Spanish as a foreign language classroom. In this study, the construct of "microgenesis" is drawn upon to refer to both, the methodological "tool" to investigate language learning instances as observed in short periods of time (i.e. minutes), and also to refer to those observed language learning instances as the "object" of study. The Sociocultural approach to Second Language Learning (SLL) (Lantolf and Appel 1994; Donato 2000; Lantolf 2000; Lantolf and Thorne 2006) underpinning this investigation sees interaction as the enabling process that becomes essential for the individual to achieve learning and development. I refer to learning as the process through which participants are able to change, transform (i.e. develop) their use and/or understanding (see Wells 1999: 111) of the target language. Pairs/trios of students were audio-recorded while collaborating to complete three language tasks in the classroom during an academic semester in a UK university. Microgenetic analysis of the data (transcribed protocols) allowed us to gain further understanding of collaborative activity and of the importance of language as a mediational tool to co-construct meaning and learning opportunities. The results show that although each instance of microgenesis is unique, there are certain characteristics and patterns shared by the various instances identified in the data set. The investigation also highlights the importance of studying discourse markers to help us identify the learners' level of regulation. Finally, we focus on a specific aspect of microgenesis that appears to be crucial for driving the learner's second language (L2) forward, and which following van Lier (2000: 252), I refer to as microgenesis affordance.