There have been a lot of schooling fish on my loc lake I fish. They'll start busting on bait in the middle of the lake and they'll hit pretty much anything you throw at them. Problem is they're all 12-15" fish. So my question is, how do you catch the bigger fish that are in these schools or are they not even there? Don't get me wrong catching a bunch of schooling fish is fun but I'm looking to catch a few bigger fish in the mix.

You throwing right into the center or past it and reeling in?

Both

Have to get through the smaller fish. Try a heavier hair jig or jigging spoon. If their are bigger fish in the school they are gonna be looking for the easier meal, the weaker injured bait that the smaller fish didn't get or was too big and now is injured.  

Two answers here. Bass tend to school by size and many schools that follow bait schools are in the size range you've been catching. Big fish rarely waste energy chasing forage. If there are bigger fish there, likely they are positioned under the fish that are feeding on the surface, feeding on any injured bait that falls below the school above. There are two ways I target those bigger fish below. A 1oz. White jig with a trailer that has little or no action and a deep diving suspending jerk or crank bait. Give the jig a few pops of the rod tip after it clears the school. Catching a fish on the jig will give you the location of the fish's depth and you can cast past the surface action far enough to get your crank to depth before pausing or jerking.