You'd think you'd remember the ponies you cower from a dark alicorn with, but I suppose Nightmare Moon took up most of their attention. Still, they live in the same town and there's only one school. So why?

In the short term, because Apple Bloom was on the other side side of the vague "class group boundary" - one of a few reasons I made her the oldest. (By Season 2, the other two have graduated into her class.) In the long term, because Scootaloo is pretty new to Ponyville and was the one who helped a rather shy Sweetie break out of her shell.

The latter part is more questionable since I wrote that, but I still like it.

It's weird, how kids will interact. They just don't hang out, and then they do, their friend groups chance at a moment's notice.

The catalyst, of course, was both Diamond Tiara and Twist getting their cutie marks. The first one made a big deal out of it, made Apple Bloom, Sweetie and Scootaloo self-conscious and more likely to band together. Twist was Apple Bloom's only friend until then, and the pressure from Diamond made her feel like they couldn't be friends anymore; we saw this in the episode. So they were just driven together by circumstance upon becoming the last three blank flanks in their class.

Don't ask about the pilot, because I didn't notice them under that table until well after I'd seen it. :V

24. Why didn’t the CMC hang out more/know each other before Call of the Cutie?
There's more than one class of foals in Ponyville Elementary. Scootaloo and Sweetie Belle were originally in a different class than Apple Bloom.

Scootaloo and Sweetiebelle DID know each other... Go watch the episode again, they were under the table TOGETHER. Applebloom, being an apple, didn't get off the farm much.