Should I let my 16 year old work or focus on school?

My boy wants to get a job at a local hardware store. Part of me wants to let him because I think building a work ethic young is crucial and he'll learn responsibility. Other part worries about his grades slipping since he's got AP classes. My old man had me working at 16 and I'm grateful for it, but times are different. What did you guys do with your sons? Looking for some perspective here from men who actually value a strong foundation.