The purpose of this paper is to examine the impact of implementation of the Science Writing Heuristic (SWH) approach at 5th grade level in the public school system in Iowa as measured by Cornell Critical Thinking student test scores. This is part of a project that overall tests the efficacy of the SWH inquiry-based approach to build students' content knowledge, argumentation skills, and interest in science to construct the foundation of science literacy with elementary school children, so that all students "become familiar with modes of scientific inquiry, rules of evidence, ways of formulating questions and ways of proposing explanations". (Contains 1 figure and 1 table.)