This study examined the social and cognitive interaction patterns of third, fourth, and fifth graders as they collaboratively read on the Internet and responded to an inquiry prompt. Data analysis revealed patterns of cognitive strategy use that intersected with social forms and functions of dialogue. Dyads that exhibited higher levels of cognitive strategy use and mutually collaborative social interactions were better able to accomplish the inquiry task. Pairs who read with little or no meaningful discussion were less successful. These contrasting cases show the range of interaction patterns that may occur during co-constructive inquiry-based online reading. Findings inform the design of instructional scaffolds to foster productive dialogue and strategic reading in online spaces.