This article documents how second language (L2) Spanish learners in an American high school formulated explicit grammar rules during three inductive lessons on the pronominal clitic "se." Following Adair-Hauck "et al." (2010), each lesson first presented a property of "se" within a narrative text, and then had learners inductively "Co-construct" grammar rules in groups of 2-3. Groups then reported back to the class, with the teacher guiding them toward a consensus. Recordings of four small groups and the whole-class discussions revealed that although successful rule formulation occurred in all three lessons, outcomes varied according to: (i) time spent on task, (ii) the distribution of turn-taking, and (iii) participants' familiarity with pertinent linguistic concepts. Variability in learners' comprehension of peer explanations was also evident, as many requested clarification from the teacher or peers. Thus, learner-generated rules were often only "subjectively accessible" to others, depending on whether references to previously learned grammatical concepts and improvised linguistic terminology could be understood. Implications for L2 pedagogy and the role of explicit knowledge in L2 acquisition are discussed.