This study explored four middle-school mathematics teachers' provision of non-examples and instructional explanations in teaching rational numbers to seventh-grade students. The data sources were 8 lesson hours of observations conducted in four different classrooms. Yin's [(2018). "Case study research and applications: Design and methods" (6th ed.). Sage] cross-case synthesis technique was used to code the four teachers' non-examples. Charalambous et al.'s [(2011). Prospective teachers' learning to provide instructional explanations: How does it look and what might it take? "Journal of Mathematics Teacher Education, 14"(6), 441-463. https://bibliotheek.ehb.be:2102/10.1007/s10857-011-9182-z] criteria were used to code their instructional explanations. The findings showed that the four teachers seldom used non-examples of rational numbers in their classrooms and provided low-quality instructional explanations to their students. The implications for improving teachers' provision of non-examples and instructional explanations are discussed.