Successful teaching entails a complex interaction between ateacher and a learner. The teacher must select and convey in-formation based on what they think the learner perceives andbelieves. Teaching always involves misaligned beliefs, butstudies of pedagogy often focus on situations where teachersand learners share perceptions. Nonetheless, a teacher andlearner may not always experience or attend to the same as-pects of the environment. Here, we study how misaligned per-ceptions influence communication. We hypothesize that theefficacy of different forms of communication depends on theshared perceptual state between teacher and learner. We de-velop a cooperative teaching game to test whether concretemediums (demonstrations, or “showing”) are more robust thanabstract ones (language, or “telling”) when the teacher andlearner are not perceptually aligned. We find evidence that (1)language-based teaching is more affected by perceptual mis-alignment, but (2) demonstration-based teaching is less likelyto convey nuanced information. We discuss implications forhuman pedagogy and machine learning.