Despite its advanced age of about 375 years, the mind--body (psychophysical) problem is alive and well, in part because it is anchored so well institutionally in schools and in research (scientific vs. interpretive psychology). This continued presence is astonishing in the light of the fact that the seed for its solution, sown in Spinoza's "Ethics," is almost as old. The solution rests on the position that there is only one substance, which, invisible, manifests itself in two attributes, thought and extension (body). By thinking with Spinoza, especially by following the ways in which Vygotsky and Marx think with Spinoza, we arrive at an approach suitable for a social psychological theory of learning that does not separate knowing (intellect, thought) from doing and emoting (body). A classroom fragment from a 10th-grade physics curriculum is used as the starting point for overcoming the body-mind problem by thinking with Spinoza.