I want thick PCB, with big fat copper through holes that can take the abuse from those new to soldering. I want the power source designed with many fail safes, for reverse the poles and putting too much voltage. Parts should be as forgiving as possible. 

There should be many modules that could either be a student made thing, or replaced with a robust manufactured IC. 

BUT the LED from their first "learn to solder" experience should still be the "power on light" in the final calculator. 

5/5 

 @134318c2 would be although great if they build modules and swapped those with other students. working together to build something bigger.
maybe even some network of calculators.