Although recent research has documented that classroom discussions may enhance students' reading comprehension, limited knowledge exists regarding the 'working ingredients' that extend students' comprehension of texts through peer discussion. This observational study examines the pre- and post-discussion comprehension of fifth graders, investigating whether particular features of peer discussions immediately following individual reading can support comprehension outcomes. The sample consisted of 102 fifth graders (many of whom were second-language learners) in 21 different multilinguistic classrooms in Norway. Altogether, 25 peer discussions were videotaped, transcribed, and coded according to eight categories of talk moves. The findings showed that the number of talk moves offering relevant arguments and counterarguments predicted significant variance in the students' post-discussion comprehension scores (controlling for pre-discussion comprehension, prior topic knowledge, vocabulary, and word-decoding skills). These findings suggest that the argumentative qualities of the peer discussions were linked to improvements in the students' comprehension outcomes.