This paper is part of a wider action research project taking place at a secondary school in South Wales, UK. The overarching aim of the project is to examine the potential for aspects of literacy and computational thinking to be developed using extensible 'build your own block' programming activities. This paper examines classroom talk at an extracurricular programming club and focuses in particular on dialogue relating to computational thinking. Learners spent a number of weeks carrying out an activity designed using the Snap! programming tool. The activity was themed around language and the task was to devise a collection of fixed-form poetry. The findings are in two parts. First is a dialogue analysis using the SEDA coding scheme. This analysis revealed a number of learner interactions showing evidence of reasoning. Second, examples of talk sequences are provided in order to examine how the reasoning identified in the interactions relate to what we may recognise as computational thinking. The paper concludes by considering how dialogic approaches in the classroom potentially have an important role to play in the process of teaching young people to think computationally. [For the Online Submission version of this article, see ED581597.]