To solve this question, we need to examine the relationship between well-known philosophers and the educational theories they advocated.

• Plato-Idealism: Plato is one of the most famous proponents of Idealism. He believed in the existence of ideal forms and advocated for an education system that encourages learners to understand these forms. Therefore, this match is correctly paired.
• Rosseau-Naturalism: Jean-Jacques Rousseau is known for his theory of Naturalism, which emphasizes a natural approach to education, where a child learns and grows in harmony with nature. Hence, this is also correctly matched.
• Plato-Naturalism: This pair is incorrectly matched. Plato was not an advocate of Naturalism; instead, that theory is associated with Rousseau. Thus, this option is correctly identified as the incorrect match according to the question.
• Dewey-Pragmatism: John Dewey was a proponent of Pragmatism, a theory that emphasizes learning through experience and practical thinking. Dewey is well-known for his contributions to progressive education, thus making this match correctly paired.

Based on the given explanations, the option 'Plato-Naturalism' is mismatched because Plato is known for Idealism, not Naturalism. Therefore, this is the incorrectly matched option.