Just from my previous CS classroom experience, the first things you should teach are the very basics. Learning the difference between a byte, integer, float, boolean, array, etc. is essential to understanding every computer language. Teach for loops, while statements, if/then conditions.
I'm reasonably fluent in several languages and variables and structures like those are core to every language including Construct. Once they get the basics of those, it's just a matter of syntax. While Construct is mostly in a language I have issues with (JS), the core concepts of how languages work allows me to code with ease.
If your intent is to teach the basics of how programming languages solve problems and to create a working game, I'm not so sure I'd delve too deep into actual JS coding. C3 can do all that without writing code. Getting structure and syntax down in a coding IDE can be pretty intimidating. While JS is a very useful language I believe I'd leave the writing code part to more advanced courses like C++, Python or C#. Those that want to learn higher level languages will take that plunge into writing actual code. Those that do not, will still have the basic concepts and could still create in C3. Besides, writing code in Construct can be fun as you usually get instant gratification and see the results. In other languages, it's mostly a thankless grind with only crunched numbers to show for it.