Stack Overflow has a slick way of encouraging users to answer questions: you don’t need to sign up to start interacting with their sites in meaningful, persistent ways. You can start building reputation and earning badges without ever registering an account. Then, when you want to make your (suddenly interesting) identity more permanent, you can easily register and keep all your previous work. The magic is in your browser cookies.
Ease of answering questions is integral to a service that aims to provide great answers to even the most obscure of the internet’s curiosities.
So it sure feels like ease of practicing math should be integral to a site that aims to provide a free education to anyone, anywhere. We would love if Khan Academy users could show up, watch a video, try our exercises, and see their badges and points accumulate without ever being asked to sign up for an account.
Later, once they’ve meaningfully scratched the surface of what Khan Academy has to offer, we could help switch their unregistered cookie account to a permanent one. Of course, just like Stack Overflow, users run the risk of losing their temporary cookie and progress by not registering. It’s a tradeoff.
Benefits
Big and obvious: more engaged learners, less users bouncing away from the “you must log in” screen, increased awareness of Khan Academy’s functionality.
Major Problem #1
Apparently it’s basically impossible to legally register for any sort of online account as a child under the age of 13. Our identity providers (Google and Facebook) know this well, and even though they don’t police the issue, their legalese is scary enough to rightfully deter most teachers and parents from registering a Khan Academy account for a young student.

Carrot or crutch? We don’t want users relying on unregistered
accounts forever.
Since it’s ridiculously difficult to register a real account for a young Khan Academy student, I’m worried that our unregistered accounts will become a crutch. Nobody is gonna go back home and get significant parental intervention before making their unregistered account permanent. They’ll wait until a cookie disaster loses all of their hard earned badges.
What’s worse? Deterring young learners so significantly that they’ll probably leave before working hard enough with their parent to get access, or giving unregistered access to everybody and waiting for a lost cookie to forget all of the user’s work?
Major Problem #2
Schools are not exactly friendly to long-lasting cookies. If they don’t actively delete them, they’ll at least share computers in problematic ways. This makes our environment much more hostile to unregistered accounts than Stack Overflow’s.

Your school’s IT administrator?
Maybe Google Apps for Education will save us all one day. I hope so. Their accounts are the reason we’ve had such success with our forward-thinking pilot school classrooms full of young students. They’re basically the easiest way for us to shift COPPA responsibilities away from us, onto schools and, eventually, into the hands of parents. But they’ll also need to save homeschoolers, the solo kids using Khan Academy for fun, and the whole bunch. At the same time, we need to do a better job guiding our young users through their various options.
Your advice is welcome
Until then, I’m having trouble deciding. Do we give everybody the ability to immediately start earning Khan Academy credentials as soon as they touch our site even if it means some (many?) unregistered users will lose their work forever?