The aim of the present study is to explore in what ways individual differences and personal experiences affect pragmatic development in an English as a foreign language classroom. Participants were 313 learners of English from 10 secondary schools in Spain. Each learner wrote one argumentative essay three times over the course of one academic year during regular classes, and a mixed-method approach was followed to examine gains in the production of textual discourse-pragmatic markers. A quantitative analysis at the group level showed that gains in the use of textual discourse-pragmatic markers occur rapidly, and these gains are sustained at the end of the academic year. In spite of the pragmatic gains, individual developmental trajectories were observed and analyzed qualitatively. Using a maximum variation sampling to select low and high generator participants, four case stories are reported. Findings of the qualitative analysis show that, in spite of the pragmatic gains, individual pragmatic learning trajectories seem to be closely related to the nature of what happens to the learners in the instructional context, together with their personal experiences.