This is how you write a transgender novel for children.
I've read (and avoided) quite a few books with a transgender youth as the main character specifically around them coming to term with their identity, and coming out to those around them. Most are either not written by a transgender author, or focus around the individuals family members, the trauma/violence, or the stereotypes of transgender people.
Most that I've read have been either good, or terrible, but until now I've not come across one that feels /great/.

I listened to the audio book version narrated by Jamie Clayton (a well known Transgender actress who I absolutely adore), and the moment it began I knew what an excellent decision it had been to get her involved.
I truly believe that having the book read by her added something that even my own brain as a trans masculine individual couldn't have done.

(To any of my cisgender teacher friends reading - I beg you to listen to this particular version with your children or for yourself. I can't even truly explain how important it is to hear these words from the mouth of a transgender woman specifically. But it makes a difference.)

A new all time favourite, 5 stars.
Sidenote:
I've been following Alex Gino on twitter for a while now and am aware that they have struck a deal to change the title of this novel to Melissa. Every copy from now on will be printed with the new name, and they encourage people to print out the free alternative cover from their site, or to engage in some light, permission granted vandalism, using sharpies or stickers to cover the old name. I took a copy of the book from my uni library to read alongside so I will be returning it with a note of the website link for the librarians shortly.