This study in the field of Second Language Acquisition (SLA) was conducted in Spanish as a foreign language classroom. The study investigates dyadic collaborative activity in computer-mediated tasks from a Sociocultural perspective on Second Language Learning (SLL). From this theoretical perspective interaction is an enabling process that becomes essential for individuals to achieve development. The purpose of this study was to gain a better understanding of the kind of tasks that might promote higher levels of collaboration and high quality collaboration in terms of microgenetic activity opportunities. The investigation was operationalised by means of the following research questions: 1. To what degree do the three different tasks in the two mediums of implementation - computer and non-computer based - support collaborative work in the classroom? a) How do learners deploy semiotic mediational mechanisms such as repetition, L1, and reading aloud in the context of collaborative activity? b) To what degree do participants engage in High Quality Collaboration (HQC)? c) What is the significance of HQC in the processes of second language learning? 2. What is the importance of the computer as a mediational tool in the processes of collaborative activity? Protocols for analysis were obtained by the transcription of audio recordings of (12) dyads/triads completing the tasks. Other instruments of data collection were pre and post task implementation questionnaires, and pre and post linguistic tests to provide evidence of interlanguage change. Results confirm 1) the three tasks support high degrees of collaborative activity - albeit qualitatively different; 2) language can - sometimes simultaneously - to be deployed by learners both as a means of communication and as a cognitive tool to achieve linguistic development; 3) the presence of the computer seems to change the nature of collaborative activity. The computer seems to offer specific benefits, e.g. immediate feedback that supports interlanguage stretching in different forms (see Kowal and Swain, 1997). However, it may hinder creativity in the case of text reconstruction tasks, for instance. This investigation highlights the Sociocultural notion of Activity Theory - in order to understand collaboration as a mediational process for language learning.