When I had to use C as part of a larger project in school it was the ability to use gdb properly (i.e. at all) that ended up predicting who would finish their project and who would not. Yeah if things get crazy and you have tons of pointer and memory related bugs gdb will show weird information but even knowing that can point people in the right direction.
Also reminding them that C isn't C++, Java, C#, etc. is a good idea. This comes up most frequently when you see someone treating a char* like a string in C++.
