Productive knowledge work and high-level literacy are essential for engagement in a Knowledge society. In the research reported in this article, students were engaged in sustained collaborative knowledge building in science and social studies. The vocabulary growth of 22 students over Grades 3 and 4 was traced, based on their entries to Knowledge Forum—a knowledge building environment used as an integral part of classroom work. It is the communal space where knowledge work–ideas, reference material, results of experiments, and so forth–is entered and continually improved. Analysis of lexical frequency profiles indicated significant growth in productive written vocabulary, including academic words. In a Grade 4 inquiry, students incorporated almost all the domain-specific terms at and below their current grade level, and most of those expected for upper grade levels (5–8) based on the curriculum guidelines. Domain-specific and academic words were correlated with depth of understanding. High correlations between student engagement in knowledge building and vocabulary growth suggest that productive vocabulary can be developed through sustained knowledge building in subject areas.
