Gamemaker has been around for a number of years now and in that time has evolved into a great platform for kids to make video games of their own without knowing a single line of code. It has similarities to SCRATCH but has probably got a little bit more depth for high school students.
If you are just looking to get started with gamemaker a friend of mine David Williams has put together a couple of tutorials that create a 'Stealth Bomber" video game. They are pitched at middle years students and very easy to follow. Take a look below.