The Education of Bet by Lauren Baratz-Logsted.
Bet is sixteen, very intelligent, but only knows as much as her limited education will allow. In Victorian England, girls aren't allowed to go to school.
Will is also 16, and though not related by blood, he and Bet act like brother and sister. In fact, they even look like brother and sister. And though they're both raised under the same roof, by the same kind uncle, Will has one big advantage over Bet: He's a boy, and being a boy means he isn't stuck in the grand house they call home. He gets to go out into the world--to school.
But that's not what Will wishes. He wants to join the military and learn about real life, not what's written in books.
So one night, Bet comes up with a plan. She'll go to school as Will. Will can join the military. And though it seems impossible, they actually manage to pull it off.
But once Bet gets to the school, she begins to realize the education she's going to get isn't exactly the one she was expecting.
This one sounds amazing! I can't wait to read it. It's released on July 12 of this year. :)
(Summary from amazon.com)