Any valid email addresses can be used to login to Khan Academy. Refer to our Teacher Toolkit's article on Setting up accounts for more information.
For under 13 year old users, there are two options -
1. Have parents create child accounts. For more details, check out http://khanacademy.desk.com/customer/portal/articles/337876 Note: The school should not create the child accounts directly. Child accounts are reserved solely for the parent or legal guardian of a child. Violation of this policy may result in deletion of the parent account entirely.
2. Create accounts through Google Apps for Education. This is a free offering for public and other nonprofit schools (most charter and independent schools are covered under this). With Google Apps for Education, you can set up Google Accounts under your own domain name (e.g., lasdk8.org) and create accounts for students, even if they are under age 13. You can choose to enable or disable features such as email on these accounts.You can use these Google Accounts to login to Khan Academy as well. Check out Google's information at http://www.google.com/apps/intl/en/edu/k12.html for more information on Apps for Education.