"Oh, the things you can find if you don't stay Behind" ~ Dr. Seuss

App Inventor is a happening application these days, so make sure you check the user forum to stay up-to-date. The latest is that when you log into the Editor Blocks, you get a new warning (bottom left box) within the usual "Do you want to run this application?" challenge:

"This application will blocked in a future Java security update because the JAR file manifest does not contain the Permissions attribute ..."

Behind the scenes, it looks like the MIT team is preparing for this Java issue by evolving the App Inventor platform (App Inventor 2) to operate entirely from your browser, without the need for the Java plug in to run the Blocks Editor and Emulator. This will give you at least one less step to navigate and hopefully, make the application more accessible to more workstations. I have had it happen where I was unable to launch App Inventor because computer lab PCs didn't have the necessary Java software installed. I'd recommend a full test run on the PCs intended for use before committing to teaching. And while I'm on the subject, by a "full test run", open and use the application to build something on the PCs you plan to use to make sure they have enough capacity to really showcase the application. It's not enough that they can open it, but are actually performant using it. I learned the hard way this past summer, using Kodu. Kodu is a great animation application, but if you try to build programs using it on under-powered PCs, understandably, kids will get frustrated pretty quickly (i.e.system too slow, unresponsive clicking, files corrupt, lose work). I was lucky enough to have my own laptop in the classroom to demonstrate how well it can work and lend it out to kids to build some projects, but frankly, teaching with this issue only risks underscoring computer programming's bad rap for being boring and too hard to learn.

You can try out the App Inventor 2 platform here. The current version of App Inventor that uses Java will be referred to as App Inventor Classic and will remain available, but after this coming summer 2014, they warn the development team's focus will be to build and revise using the App Inventor 2 platform.

Another thing to keep in mind is that projects created between platforms are not portable, unfortunately. Meaning, what you create in App Inventor Classic cannot be opened using App Inventor 2 and projects created in App Inventor 2 cannot be opened using App Inventor Classic.I'm going to spend the next month working in App Inventor 2 to test it's stability; MIT warns that while it's under development to finalize, there may be times when things don't work as you'd expect or that your projects might break.

Which is a good reminder that the teachable lesson is: we're all experimenters when it comes to learning to program. To paraphrase another favorite Dr. Seuss quote - "Don't worry! When things are happening, make sure you're happening too!".