Science learning is important for the well-being of individuals and society. Acquiring the knowledge necessary for success in science is not easy because science involves relational thinking, or the ability to abstract and generalize from similarities between concepts. Using relational words, or shared linguistic labels that identify commonalities between at least two entities, has been shown to promote relational thinking. However, research has yet to directly link relational language and science knowledge. Thus, my dissertation examined the nature of this link by examining whether children's relational productive vocabulary predicted their science knowledge above and beyond other factors, such as general vocabulary, demographic variables, and science attitudes and behaviors. Results revealed that, contradictory to my main hypothesis, children's relational vocabulary size did not predict their science knowledge above and beyond general vocabulary and demographic variables. Instead, relational vocabulary was linked to science knowledge by serving as an intermediate step between children's science talk frequency and science knowledge. In brief, the findings from this study are a key step towards fully understanding the mechanism(s) by which relational language drives changes in science knowledge. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://bibliotheek.ehb.be:2222/en-US/products/dissertations/individuals.shtml.]