mstone326 wrote:

Scratch games aren't always simple. Look at this Griffpatch example and the code in it. It is FAR from simple. Scratch can go as far as you want it to. It will run into issues with lag and performance if you have forever loops all over the place running when they aren't necessary.

Here is a game called Scratchnapped. Look at the code, this is far from simple. I am still a little gray on the “Serious” game definition.
https://scratch.mit.edu/projects/10118230/

All you really need to consider is the question: When kids are learning Scratch and starting with simple tutorials, is it reasonable to then have them modify the simple game they have rebuilt to fit a serious theme (environmentalism, social issues, etc.)?

Yes. Absolutely

Had a thought for you as well if you are just really planning on focusing on the message or the Serious part of the game. You could create a 2d game engine for the students to use with placeholder sprites. So the main sprite is a rectangle that interacts with level sprites you could create generic simple block versions of. They could then, without dealing with any code except for anything extra they want to add or alter (changing jumping height, more or less gravity, etc), they could focus their time on the artwork, message and execution of their project.

Less of a coding project and more of a variation started from a simple game engine. I did that with my students last year. I created a simple game engine, then asked them to change the graphics, alter any of the gravity, jumping, etc code they needed. Add a title screen and a game completion screen. But the bulk of the code was given to them.