Heart of a Samurai by Margi Preus

School was where it would all begin. Manjiro had never been to school. He didn't know how to read and write even his own language. Now he was going to learn to read and write in English, and to do that, he would have to attend class with the little children. Sixteen-year-old boys like him went to different schools. If they were smart enough, they could go to the Bartlett School of Navigation. That place was for students who excelled in school, who were likely to go on to be whaling captains, ship owners, important people. At Bartlett they could learn mathematics, surveying, and, most important, all the secrets of navigation. That was the school Manjiro longed to attend.

But he began his education at the Stone House School, where he studied arithmetic, learned the alphabet, worked at reading and writing English, and practiced a thing called penmanship.