The data consisted of students’ documents written during the MEA, classroom
observations, and video-recordings of the students' presentations of their models. The written data included students’ modeling drafts, conceptual tools and written presentations. It should be emphasized that the students were asked to write down everything, so that drafts, sketches and final solutions could be collected. The video-recording included students' oral presentations of their models, researcher interviews and class discussions. Transcripts of these videotapes were used along with students’ written data to assist researchers in the analysis.