As a child, Will Wright was educated by the Montessori method. Montessori learning is basically learning through experimentation; self-directed interaction with objects and relationships. This is the sort of learning that permeates Spore.
Players intuitively learn through their experiments basic concepts of structural biology; how the shape, size, and orientation of various body parts combine to form aptitudes and behaviors.
In the tribal and civilization stages, players intuitively learn basic concepts of government. They learn about resource management, the necessity of defense, diplomacy, and civic engineering.
In the space phase, players are exposed to the first detailed 3-D model of space -- an achievement significant enough to earn Wright an invitation to demonstrate Spore at NASA. Kids and adults can be exposed to concepts like black holes, quasars, asteroid and ice belts, and perhaps the many phases of a star's life cycle.
Of course, like with any teaching tool, some guidance is good. For example, Spore begins with the panspermia/exogenesis
More generally, Spore provides inspiration for learning; enthusiastic questions which parents and teachers can use to open broader or more detailed lessons. After a child has equipped his or her creature with horns, spitters, plating, or claws, you can use that to open discussion of the countless defense mechanisms not included in the game. As children paint their creatures, you can introduce them to concepts like camouflage, feathers, or exoskeletons. No matter what they're playing with in Spore, it's a great occasion to point out the wondrous variety of life and beautiful logos which pervades our universe.
Spore is one of the best examples of potential for educational games. Like trips to museums and zoos or time spent out with nature, it can be an invaluable inspiration for learning. Learning should not always be fun, but it certainly can be.
This sort of educational value is an important part of the future of video games as they become increasingly mainstream. No work of art or product is free from social responsibility.