Alex isn't stupid. He knows how the world works. He gets taught as a kid that whatever the enclaver kids are into, you pretend to be into it too, you spend your free time learning as much as you can so that it looks to them like you're effortlessly good, and then a year later when they make fun of it you make fun of it with them. You don't get attached to your siblings, not when they're probably going to die. He sees it at the public school, too; mundanes aren't any better, always choosing the weak kids to push around.
He feels bad for them, but there isn't much he can do. Not without power.
(He tries, sometimes. He knows it's stupid, but it's hard to not. So maybe he's a little sentimental. Sue him.)
It's better when they're a little older; he starts dealing drugs on the side when he's twelve, partly for money but mostly for connections. He's going to miss it, in the scholomance. It's a good role for being on everybody's good side.
His affinity is long-range divination. It's-- not bad, if he lives it'll be great. The problem is living long enough for it to become relevant. His parents pull in favors, convince people he's an investment rather than a liability. He'll be doing the same thing, once he's in.
He's small for his age, which is good. More weight allotment. He's using almost all of it on extra resources for Mexico City. He'll be working for them for a year, too. It's not a bad trade, all things considered; people would kill to be in his spot. Possibly have, in the past.
He works hard, once he's in. Studies and carries things and helps with projects. Mostly reserves his help for people he wants the favor of, people stronger or smarter or better-connected, people who have something he wants, but he's still the same bleeding-heart who snuck his little sister extra dessert and sometimes he'll do math homework for the obviously-doomed. He keeps track religiously of who's good at what, who needs what, what terms everyone is on, the complex web of alliances and enemies, friends and lovers. And it's easy, then, to be the person who everyone goes to, the middleman, the matchmaker.
And he flirts, because he's cute, and that's a resource too. People who have a crush on you will try harder to earn your favor; dating can be stronger than an alliance, if you stop tracking debt with each other.
(And maybe also a little bit because he likes it, likes the attention, the showing off. Likes having that little bit of power.)