School fish that become active - why do they occur?

[Spoonminnow]

The topic about crappie jumping over and rolling on lures near the surface is something I've seen for decades at least a few times a year. Those fish are always in a school of fish that for some reason can be provoked to turn on big time or that are already in a super aggressive mode. Are there conditions where this happens or is it just a freak of nature?

I've seen this in all seasons. Once I discover school by accident, I can cast to the same spot 15 yards wide or less and clobber them or find the school under the ice and take fish after fish from a series of holes cut in a large circle. (At one time my partner and I caught over 60 crappies by going from hole to hole.) Once the school turns off, that's it - no more fish.

The other things I've observed is that this unusual bite is always seen in shallow water or close to the surface over deep water and that even though my boat passed near or over the school with my trolling motor, the fish would still turn on.

Other than in spring, I guess the super school-bite will forever be a mystery and unpredictable - a good thing for most waters that see a lot of harvesting.

[kickingback]

With large schools of crappie they are feeding on the bait fish usually. When one or two crappie start agressively attacking shad or your lure, the other crappie begin getting agitated by the fish moving around faster to get the bait. Then the frenzy starts and the fish are all active to eat. It happens more often than you think. Once the fish have had their fill of the bait and the action slows down, so do the crappie feeding. They are usually still there but not biting as much due to the feeding frenzy.
I see schools all the time on my home lake and I follow the ripples and troll through the mass and catch many slabs this way. After the bite slows down, I usually move to another spot for a while and try the same location later to see if they are still hanging around structure near where the school was.