The honest answer is both, because school and shoal describe two gears of the same social behaviour. A shoal is a group staying together loosely, each fish minding its neighbours while doing its own thing. A school is that group locked into formation — same speed, same direction, turning as one. Boeseman's rainbowfish spend most of their day in the loose gear and shift into the tight one whenever the situation asks for it, and watching the shift tells you a great deal about how the tank feels to them.
The default: a loose, busy shoal
In a settled tank, Boeseman's hold together as a shoal through the middle and upper water. They cruise the same stretch of tank, drift around plants in the same general direction and regroup constantly, but individuals break away freely — a male sidles off to display, another drops to investigate food, a third rests briefly in a plant's shade. The group looks like a constellation rather than a parade, always recognisably together, never marching.
The shift: schooling under pressure
Startle the group — a net enters the water, a shadow falls suddenly, a boisterous tank mate charges through — and the shoal snaps into a school. Bodies align, spacing evens out, and the whole group wheels away in one synchronised movement, flashing blue and orange as it turns. The same tightening appears in healthier moments too: a confident group sometimes cruises the tank's length in formation for no reason beyond momentum, and feeding time can briefly organise them into a moving front at the surface.
Why the group is not optional
Boeseman's are built socially from the ground up. A single fish or a pair lacks the audience for display, the safety of numbers for confidence, and the rivals that spread male attention thinly. Lone Boeseman's characteristically hide, lose colour, feed timidly and succumb to stress-related illness at rates their grouped siblings never approach. In a proper group — several individuals, with more than one male — the shoaling behaviour described above appears within days, colours strengthen, and the mid-water of the tank becomes the liveliest zone in the room.
Space and tank mates shape the formation
Boeseman's are strong, active swimmers reaching a substantial size, and their grouping behaviour needs length to express itself. In a long tank the shoal stretches out, cruises, reforms and displays across real distance. Cramped quarters compress the group into permanent tightness that looks like schooling but is actually crowding, with the stress to match.
Choose tank mates that let the shoal stay loose: peaceful fish of compatible size and water preferences, nothing fin-nipping and nothing large and predatory enough to keep the group permanently alarmed. Fast, frantic species competing at the surface can also keep Boeseman's keyed up, while calm companions let the rainbowfish own the mid-water and settle into their natural loose rhythm.
Reading your group day to day
Judge the tank by which gear dominates. Mostly loose shoaling, brief schooling at genuine surprises, eager converging at feeds — that is a group at home. Permanent tight bunching, hiding, or individuals exiled from the group are your early warnings, to be answered with water tests, a tank-mate audit and a count of the group itself before anything else. In KinsLe Care Teams, a weekly group check — numbers, colour, who is being excluded — can be assigned and timestamped, so a Boeseman's shoal that starts to tighten up gets noticed while the cause is still easy to fix.