Creating and critiquing explanations of phenomena is a significant goal of many scientific disciplines and therefore also a learning goal of science education. A significant source of explanations is science textbooks; however, the large corpus of text in textbooks means that manual review of explanations by individual researchers is extremely time consuming. In this paper, we introduce a text-mining approach for identifying legitimate and illegitimate forms of teleological explanations in school physics and biology textbooks. An ongoing debate exists about the legitimacy of teleological explanations, that is, explanations which account for a phenomenon by reference to a final end, purpose, or goal. Until recently, researchers tended to view teleology as an illegitimate form of scientific explanation. Recent theoretical cases in biology and physics have emphasized that legitimate teleological explanations exist in both domains. Eight science textbooks used in England and internationally were analyzed for instances of teleological explanations. The analysis reveals the efficiency of the text-mining approach for automating the analysis of textbooks and its potential as a research approach in science education. In considering text mining as a research approach, we report terms that are likely to be associated with legitimate teleological explanations. We found that legitimate teleological accounts are used by textbook authors, and we present novel categorizations of these forms of explanation. We argue that text mining can be a useful approach in science education research and our findings suggest guidance for both textbook writers and teachers related to their selection of legitimate explanatory forms.