Sixteen-year-old Clementine will die the day she turns twenty. The Extraction Test is her only shot to prove she's worth keeping alive.
I like this line. Names the character right away, what she wants, and what she needs to do to get it. Don't change it.
The test instructors look for intelligence, obedience, and an elusive quality they call Promise. When up against hundreds of other kids who want off the planet Surface, Clementine's not sure anything she does will be enough.
Why is surface capitalized? Is the planet named Surface? Or did you mean to say planet's surface and made a typo? As an agent, I wouldn't know.
Why does Clementine doubt herself? What's her evidence for the doubt?
But it happens. They pick her for Extraction. For her prize, she gets to ditch a dangerous life of labor in the Surface slums and move to the underground colony in the Core, where Promising individuals live in luxury. Down there, she doesn't have to ignore the hollow ache of hunger. She doesn't have to worry about dying from the moon's poison like kids do on the Surface.
I don't think you need "for the prize" -- that's implied.
And now I see that Surface is the name of the planet, but maybe you can reword that first mention so it's doesn't look so victimized.
I think you might be spending too much time on the backstory. I want to know about the present-time story. What happens after she's picked for extraction?
There's only one thing she misses: Logan. The boy she never wanted to abandon. Her best friend, her everything. She swears she'll find a way to save him before he dies. Except, no one tells her there's a price to her new life, and it comes in the form of an injection serum meant to subdue Core civilians. Clementine doesn't get to keep her mind.
I don't think "The boy she never wanted to abandon is necessary". It's implied when she you say she misses him.
Likewise injection serum. You can't inject a solid into your body (usually).
And again, not sure what the story is. You started with Clementine wanting one thing, and now that she got it, she wants something different. Think high concept -- if you were describing this as a movie, what would the character want for the majority of the movie and what does she do to get it.
My young adult novel EXTRACTION, complete at 60,000-words, will appeal to readers of both science fiction and dystopian. Thank you very much for your time and attention.
No dash between 60,000 and words.
I don't like you saying "it will appeal to..." it sounds presumptuous and full of yourself. Just say the novel is of the sci-fi dystopia genre.