No fish are going to school in your tank. They exhibit that behavior to avoid predation. When they realize there are no predators in your tank, they won't school.
That said, if I had a 300g I would add a huge group of anthias.
I would agree 100%. I have tried chromis in 2,000, 6,000, 10,000, and 12,000 gallon tanks, and always end up with around 10% left through gorilla warfare. Never had any luck. Any kind of dart fish I've kept in groups has always just paired off, and usually harassed the rest. The cardinals I've kept would tolerate groups, but never really interested me, personally. I have kept hundreds of anthias, and dispars, lyre tails, or sunsets would be my recommendation, with all small females to start. You can try P. pascualas/tuka if you have the time to provide them with naups every day. They will eventually start turning male and harassing the subdominants, but they have done the best of the 9 or 10 species I have kept in groups. They will not "school," but they sure look nice in groups (the chromis pictured are what is left of 100).
Fusiliers will school really well, but almost all species get too big for most home aquariums. I would love to try some neon fusiliers (P. tile) again, but they are very hard to find in the hobby, and probably still too big/active for a 300.