Spectra Shock, Iron Blade, and Cupcake Frosting are just normal ponies - until they find out that their teacher, Silver Lane, is not just a school teacher. They think that their lives are perfectly normal - and the discovery of their teacher's true identity can change it forever...
What's strange is the weird powers that the young ponies start to get. Then when Silver takes them to her "camp", the ponies there explain that everypony at camp is related to a god or goddess - including the three new ponies.
However, the three new ponies have discovered something else - that a danger is rising above all the gods and goddesses of Equestria. Shining Armor, the god of battles and defenses, has come to help the half-bloods train for the upcoming battle. But why do Spectra, Iron, and Cupcake keep receiving messages from Cadence, the goddess of crystals and marriage, to help Shining Armor? Somepony is behind all of this... but who?
(Labeled under "Romance" for parts between some of the ponies! X3)
This story's looking good so far! You may want to add the name of the pony whose POV is being used in the beginning of the chapter in addition to the chapter name, because most readers don't read the chapter titles and that gets confusing, but it gets figured out by the end at least.
I hope you give more information later... Like how this trio came to know the Mane Six and CMC (were they recruited by Babs in her own town? Are they yet another subdivision?) and how the heck a Pegasus and earth pony can hold onto a weapon long enough to wipe out a hoof full of changelings on a rapidly moving vehicle.
I haven't seen very many grammar mistakes worth mentioning so far, though, so good for you! It's rare to find a story with a fun theme AND a good writer -that isn't a oneshot- these days. I may be tempted to write a story or two in this universe myself, if that's okay.
Slow down and give detail. A character's description should be sprinkled for the readers sake, not all dumped on us at once. Especially not before the story begins. In less than a thousand words we already have the main characters being attacked...and what do we know about our setting?
Sometimes setting up action right away is a good way to book a reader. But since it happened at the end of the chapter I don't think that was what you were going for. Since that is the case I really have to tell you to set up the surroundings some before there are life threatening attacks. Right now I wouldn't feel anything if a changeling ripped out cupcake's throat. I wouldn't even know where her blood would spray because I have no idea what their surrounding look like!
Sorry for getting a bit repeative.
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so it might not be the best I could actually do. Sorry though 
Well, this was made quite a while ago, and I haven't exactly thought of that before. At the time, I was just interested in actually getting the story into play
Oh, and they're able to fight them on a "rapidly moving vehicle" because the bus pulls over and stops. for a while.
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Well, as for the setting, didn't I say Manehattan? And the camp is in the Everfree Forest. For the characters... Yes, I'm sorry that I didn't describe them all that well. Like I said to CloudySkies, this was made a while ago (two months ago, really) and it isn't my best. So I'm sorry if it's kinda bad
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Just knowing the city is not enough, act if your reader doesn't have extensive knowledge of the location. Part of the setting is the scent, the smell, the taste, the sound, and the feel.
You don't need to give all of those, but sight at the very least needs to be stimulated. I'll give just a short example of Manehatten for fun, typed on my phone.
Imagine Manehatten if you will, it's spiraling towers so graceful and high. It was seen as the marvel of the century, a city that grew up into the sky instead of across the vast plains of Equestria. But that was what somepony would see only if they did not live there themselves.
For those that lived there, it was a claustophobic jungle of iron trees and concrete floors.
Never mind, i got bored. But as you can see...
OH MY GOSH OH MY GOSH OH MY GOSH calm down cupcake
SEQUEL!!! If you don´t continue this series