I go to two homeschool co-ops, and they are so much fun! Co-op is basically a half day, one day a week school for homeschoolers. A lot of homeschool Moms get together at a church or other large building to teach each other's kids for a few hours. The Moms in the group offer different classes they can teach, then the kids sign up for the classes that they either need for high school credits (older kids only) or they need for their regular schooling or that just interest them. Co-op only goes for about eight to twelve weeks in the spring and then again in the fall, depending on the size of the group and when they want to start. We go to one co-op on Monday and one on Friday, but they could be on any day of the week, depending on what is most convenient for the group.
If you are a homeschooler and never been to a homeschool co-op, then I advise you to try it out. It is a great tool for meeting other homeschoolers in your area and it helps Moms share their skills and talents so that the kids get to learn certain things that their parent(s) maybe could not provide. The Moms meet new friends, the kids meet new friends, and it is so helpful for many homeschoolers across the country. You can usually find homeschool co-ops near you on the Internet.