Homeschooling typically offers a more formalized curriculum depending on the parents. Unschooling looks at life itself as the format through which children can learn. For example, a homeschooling family might choose a workbook or lesson plan to learn more about insects while an unschooling family will take a walk in the woods and learn hands-on. Not that homeschooling families do not choose hands-on learning but unschooling families choose this far more often. While both options provide for a flexible learning environment, the unschooling option can be made more child-friendly.
Children learn best when they are ready and when learning is made fun.
And that is what unschooling is about. An unschooled child also is able to proceed at her own pace. State requirements must be met in terms of taking formalized tests, and that varies with each state, but it is easier to advance at your child's maturity level with unschooling. Another example would be the age at which children learn to read. The formalized school environment will demand it by a certain age as may a homeschooled environment.