OP, keep in mind that some people do not try hard in academic settings, but work very hard in other settings. I could never study hard in school setting and got by barely to get degrees and understand concepts good enough to get C+s or Bs, but was able to work very hard with dedication in business world. The fact your kid is working hard shows he is not a lazy kid. Getting good grades is not for everyone.
I thank my mom who signed all permission slips to skip school. Lol