I just read through the pong tutorial, which is also the first Blockly tutorial that I've read. One thing that caught my attention was the use of short, non-descriptive variable names. As a software engineer, I find that to be a generally poor practice, especially when teaching others to program. The variable should be descriptive enough to understand it's usage without having to consult any other code. All programmers (myself included, occasionally) eventually get lazy and start shortening our variable names, but that should not be how you start your programming career. Teach good programming practices, then let them go off and learn bad practices on their own.