Code Avengers: High School programming the MARVELous way (blog.codeavengers.com)

This has some really interesting problems to solve. You should give it a try even if you know how to program.

I saw this a couple of weeks ago, and they have really improved the user experience a lot than before.

Keep up the good work guys!

This site does a great job of making JavaScript fun to learn. The challenges help you remember what you have learned. I highly recommend trying it out!