Science is an important domain for investigating students' responses to information that contradicts their prior knowledge. In previous studies of this topic, this information was communicated verbally. The present research used diagrams, specifically trees (cladograms) depicting evolutionary relationships among taxa. Effects of college students' and 10th graders' prior knowledge on their ability to reason from information depicted in cladograms was evaluated in two ways: (1) By keeping the hierarchical branching structure constant while manipulating whether the taxa-targeted common misconceptions about biological classification or were unfamiliar; and (2) by keeping the targeted misconception constant while manipulating the strength of the evidence countermanding that misconception. Students demonstrated more sophisticated reasoning when (1) the taxa were unfamiliar, so they had to rely on the diagrammatic information presented rather than their incorrect prior knowledge, and (2) stronger evidence contradicting their incorrect prior knowledge was presented. Students' challenges to correctly interpreting evolutionary trees included lower level of schooling and greater strength of the misconception. College, but not high school, students showed some ability to transfer their better reasoning with cladograms depicting relationships among unfamiliar taxa to cladograms depicting taxon relationships that contradicted their everyday conceptions. Implications for improving biology education and overcoming misconceptions are discussed.