how to protect authorship?

What is the suggested method of protecting ai2 apps that will be distributed for education purposes?  I have been reading about copyright and copyleft.

GNU General Public License

There is no suggested method; if you need protection consult an attorney.  Copyright law is exceedingly complicated.  In the US, in other countries the basis is different.

Here is 'advice' from the US Copyright office, it might help you:  http://www.copyright.gov/fls/fl108.html  that may or may not apply to your intellectual property.

Here is another one:  http://copyright.gov/circs/circ61.pdf 

This post is NOT legal advice, it just tells you where you can look for more information to decide what you want to do.  Consult an attorney.

Steve's being properly cautious in clarifying that he's not giving legal advice.

Personally, I like to distribute my educational software under GPL.  That's a good choice for people who want to share their work, and one that I advocate as an FSF board member.  But you might have different requirements.

Note that the licensing decision is completely up to you:  If you read the App Inventor terms of service (linked from the App Inventor web site), you'll see that neither MIT nor Google have any proprietary interest in the apps you create.