I have two teenage daughters and I transitioned when they were both in High School... and I really wish I could tell you it's been plain sailing. In truth, it's been an absolute nightmare. A nightmare caused by other people.
If I were you, my first priority would be to think long & hard about whether to be stealth or out, depending on which option you think would be better for you & your son. Would it be better to be stealth and present yourself as a father? Could you deflect questions about his mother by saying that it's a sensitive issue and you don't discuss it; or that you used a surrogate; or simply that she isn't in your lives any more? Would your son inadvertently sabotage that by telling people the truth? What happens then?
Or would it be better to just go in with all guns blazing right from the start? Pick a school based on its diversity policies, and then tell the school that you're trans and you need them to do their duty in protecting your son from any potential bullying or harassment. Ask them to educate the kids regarding the different types of families in the school, and ask them to stamp down on any bullying that might happen.
Whatever you choose, you'll encounter all sorts of unexpected situations and you'll have to take each one as it comes & respond accordingly.
If you choose to be out you might be lucky and find a very accepting environment for your son... or you could be setting yourself up for years of othering & bullying; malicious playground gossip (those mothers at the school gates are a nest of vipers at the best of times - as are some of the dads!); being excluded from school & social events; your son being 'forgotten' when birthday party invitations go out... in other words, if you're out you (and your son) could potentially wind up being treated like second-class citizens. I wish it wasn't so, but schools are cliquey and a lot of parents regress to the same cliquey behaviour they used in childhood when their own kids go to school. Parents who were bullies when they were children often grow up with a tendency to pick on other parents at their kids' schools... because that's the only way they know how to behave in a school environment.
I can also guarantee you that there are other parents at every school who are a lot 'freakier' than you might be (you'd be surprised what goes on behind closed doors!)... but the reason why they and their kids don't get bullied for it is because they manage to hide it, i.e. they're stealth. That's an important lesson, and one worth considering.
You have to do what you have to do in order to be happy within your own skin. And being happy within your own skin will no doubt make you an even better parent for your son. But if he gets bullied or teased, or if any of this messes up his life - it will not be your fault; it's the fault of the bullies who pick on him. But that doesn't stop you from feeling in some way responsible and wishing things could be different.
Just remember: you don't owe anyone an explanation for how you live your life. You can refuse to answer any questions you don't want to answer. Nosy strangers have no right to any details about your personal affairs.
