They used wooden balls, wooden discs, water colors, wood glue, hot glue, and he drilled holes so they could put the dowels in as stands.
While the sizes of the planets are not to scale, they are representative of their relative sizes (for example, Venus and Earth are about the same size, etc). The distance of each planet from the sun, however, are to scale based on their average distance and the size of the board. I eventually met up with them and helped paint a couple of the planets while Little Sis worked on painting the others. It was hard for me to let go and let her do a good portion of it.
I think it turned out great. I dropped it off at school today, and managed to get it into the school office before I knocked Pluto out of orbit. I was able to do a quick re-glue, since it only came out of the base, which was still glued to the board.
Jupiter (and the alien egg spaceship)
Mercury, Venus, Earth, and Mars (and the asteroid belt)