The purpose of this study was to identify and describe teaching actions--embedded in the "Science Writing Heuristic" approach, a systematic teaching approach that integrates literacy instruction and argument-based inquiry learning of science--supportive of the cross-disciplinary literacy expectations necessary to compete in the 21st century. This article reports on qualitative findings from a mixed method longitudinal study conducted with 32 elementary teachers and over 700 students. The analysis of multiple layers of data identified two essential teaching action categories supportive of cross-disciplinary literacy skills development among students: (a) building an inquiry-based literacy community of social learning and (b) purpose setting, with a gradual shift of responsibility from the teacher to the student. A model is presented that emerged from the data and visually illustrates how teachers and students explore the purpose, function, mode, and audience within critical science-literacy events while engaging in science content learning.