This dissertation describes classroom-based research on talk and learning. The educational problem I addressed is underachievement. My research addressed a group of thirteen to fourteen year-old ESL students in Portuguese classrooms, with a view to foster their speaking skills and turn them into successes, through the use of scaffolding techniques. The theoretical framework for my research was largely informed by Vygotsky's theory of socio-cognitive development, complemented by contributions from the Neo-Vygotskian school of thought. But, given the specifics of its context, other research traditions also receive attention in my literature review. Among these are research on the importance of context and ideology for my study, and research on the grammar of spoken English. The research design adopted for both the pilot and the main research study was a quasiexperimental 'pre and post' approach, intended to test the outcomes achieved by the use of specific scaffolding strategies. The analysis looked at scaffolding already being used by the teachers I worked with and identified weaknesses and possible ways of scaffolding the learners, with references to the literature reviewed. I then identified and discussed these additional possibilities with the teachers and recorded and analysed their subsequent work with the learners. A tentative conclusion is that it is possible to foster the speaking skills of underachievers in the contexts under analysis, through a more sensitive deployment of scaffolding strategies by the teacher. While more research is needed in this field, it is hoped that my study will make a valid contribution to the teaching of English, as a foreign language in non-English speaking countries.