There are lots of great online classes available now for older kids (and parents too). My favorite is ITunes U. I download the lessons and listen in the car. – You can even set it up to listen on your computer through Itunes or on any MP3 player.
Some others that were listed in Family Circle recently include:
Einztein.com – A mix of schools, museums, and more. It even includes some social networking features to let you meet and share with other students.
AcademicEarth.org – An indexed set of linked courses available around the world.
LiveMocha.com – A resource for learning a language. Currently there are 35+ languages available.
These great resources aren’t just for kids. Even college students and parents can use these sites to study up on subjects of interest.