Find That Book

I remember reading this probably in the late '60s or early-to-mid '70s in the US, though it might have been published in the '50s. A man I'm fairly sure is referred to as "the professor" is fixing up a school bus to go out for a summer-long research trip. The mothers in the neighborhood all decide that this would be a great thing for their children to participate in, and the professor agrees to take the kids and fixes the school bus to accommodate the kids also. I think one of the boys may have been named Oliver -- called Ollie? -- and there was definitely a chapter where the Professor is surprised to come across one of the boys practicing a musical instrument (some kind of wind instrument, I think) because there has been no sign of this previously in the summer; the boy doesn't like practicing because he isn't very good at it; he knows what the instrument should sound like when played well and he can't seem to do it. And the book ends at the end of the summer with the bus going home and the families welcoming the kids back.

It is not part of the Magic School Bus series in fact I don't think it's in a series at all, but I associate it in my mind with Mr. Popper's Penguins.

Can anyone please help?