That's the Way to Do It! Jerome Beatty Jr., The Tunnel to Yesterday (New York: Avon Books, 1983).

Occasionally I'm just going to have to cheat: this isn't a science fiction book, it's a fantasy time travel. Sam Churchill volunteers for a dig near Plymouth Rock and finds himself back in 1620 just before The Mayflower lands. His presence creates (and three hundred years later clears up) a local mystery. I like the book because the archeology is depicted realistically, nothing comes easily (Sam has to learn Naugawump the hard way) and the adults around him, his employer and the archeologist, treat him like a person. As well as for lines like this:

"It was too late for Sam's parents to say no and to they had agreed to let their boy go off to a strange town for the summer. They gave him advice, warnings, fifteen dollars and a new no-wind battery wristwatch. They put him on a bus to Boston where he changed for the local to Plymouth." (11)