Jfantj,
It’s a good idea for your son to learn how coins are minted. It’s the starting point for any of us. Once you learn the process of how they are made, then when you see something that is off you ask yourself “could this have happened during the minting process?”. Then you can start seeing what is damage because it couldn’t have happened at the mint. Anything that happens the second it leaves the mint is damage. Here are a couple of resources for him to watch.
Also if your son is a reader, there are several good books to start his numismatic education with. Looking back I wished I had started with a logical process of learning in sequential order starting with how they are made. Then working into errors and learning about the types of coins I am interested in. If he is a reader two great books for him to learn both some history and the minting process, and also both authors are active on these threads, are:
From Mine to Mint - Roger Burdette (RWB on here)
The History of the US Mint and it’s coinage - David Lange (DWLange on here)
Hope this helps. Numismatics is tough. I have graduate degrees in both economics and statistics and I think this is harder 😂