One area might be clean energy.
You could divide it up into wind, solar thermal, and non-dam hydro. To make it competitive between rich and poor schools, have them make wind turbines and solar thermal units from stuff they pull from a dump, so they're recycling too.
An obvious start would be to make their own schools entirely energy self-sufficient, and then to start making money from power generation through net metering.
Another area could be potable water.
Which school can use low tech recycled materials and clean energy to reclaim the most dirty water, extract moisture from the air, or desalinate sea water?
For the less clever, more brute strength types, sandbagging.
Can you protect your community from flooding by building up the levee?
Which school can make the most earthbag housing for people displaced by flooding, fires, and drought?
You could add more hoops for them to jump through to add some "strategery," but this would also appeal to desire to contribute and be a "superhero" innate in most kids.
Instead of saving the game, they could save the world.