We always attempt to make learning as enjoyable as possibly, figuring if they realize they can enjoy it they will do more of it. Some things lend themselves to this rather easily, such as cooking when learning fractions and weight. Other things need a little more help, such as when learning the Constellations or Flower Anatomy.
Constellations can be difficult. They did their school work during the day so when evening falls and the stars come out, if you even live in an area you can actually see stars, getting the kids to do additional "school work" can be difficult. We like to incorporate it when we go camping or driving back from a trip we can stop and do a little astronomy lesson. But aside from actual field work there are other fun ways to learn about the heavens. Take for instance the Constellation Flash Cards, these can be used in numerous ways to help children remember the specifics. Print out 2 sets and use them as memory cards for single players. Or play your own version of Guess Who. Or you can do what I did and print them out and blow them up on your copier. Hang them on the wall in your school room next to your solar system poster. I love versatile learning tools.
If you have a computer learner you can click on over to My Schoolhouse for some online interactive lessons on everything from Photosynthesis to the Human Skeleton to Magnets.