This is a children’s book that was read to us in class during the mid-1970s, but I felt it was from an earlier era. In it, a brother and sister leave school and join their father and his friend (a man) on a yacht in the tropics for a year. Their father’s friend acts as a tutor. They do their lessons on ship. They swim in the sea and eat breadfruit. I was impressed at how mature and capable and adventurous the kids were.
I never read the Boxcar Children books, but after seeing the recent animated movie I was doing a little research on the series. Your summary sounds like one of the plot summaries I came across. It may be BLUE BAY MYSTERY
This may be Alice Berry-Hart: To School in the Spanish Main
Some of the details are slightly different, but this could be the sixth Boxcar Children book, _Blue Bay Mystery_, first published in 1961. The four siblings travel by ship to a tropical island with their grandfather and the grandfather’s friend. They do schoolwork on the ship and eat breadfruit once they get to the island.
This sounds very similar to the plot of Blue Bay Mystery, one of the Boxcar Children books by Gertrude Chandler Warner.
I just got through reading “Blue Bay Mystery” and that is the one! Interesting that my teacher only read is #6 from the series, and I never knew it was from a series! Also, my daughter read these books when she was a little girl, but she only read up to #5, so she didn’t read this one. Thank you everyone for helping remember the name of this book which has haunted me for years!