A student in my programming languages class pointed me to the Python Challenge site. It looks like a great way for someone new to Python to test her skills and learn new ones.
It’s a riddle site in the style of notpron, but one where solving each riddle requires a little bit of Python programming. The solutions are entered by changing the URL of the current page to take you to the next riddle page. The problems are “designed to be solvable by Python newcomers and yet challenging even for Python experts.”
This type of site could be a good educational tool for many subjects.