A parent (thanks Dr. E) found this old projecting microscope at a microscope store in town. The optics are arranged upside-down relative to normal: the light is at the top and the objective lenses are upside-down and below the slide. The light coming through the objective is reflected onto the screen using a simple mirror.
It needs a dark room to see some of the more detailed, lightly stained. However, higher-contrast slides show up reasonable well in our classroom, despite its large, unblocked windows.