Shoaling, not schooling
The distinction matters for how you set up the tank. Schooling fish move as one body, turning together in tight formation, and look stressed when kept in small numbers because the formation is their defence. Endler's livebearers are shoaling fish instead: they are genuinely social and prefer company, drift in the same general area, feed and scatter together when startled, but each fish picks its own path moment to moment and the group has no fixed shape.
In a planted tank you will see the pattern clearly. The group loosens and spreads while grazing, tightens briefly when a hand approaches the glass or a shadow passes, then relaxes and fragments again, with males peeling away to display and rejoining without ceremony.
What the males are doing on the edges
Much of the apparent disorder is courtship geography. Males spend their day working the edges of the group, displaying to whichever female is nearest, chasing her for a few seconds, then losing interest or being displaced by another male. Females travel in looser, calmer company, often a little lower in the water, and young fish weave through the plants at the margins where they are harder to spot.
Because the males are so persistent, the group's balance matters more than its exact size. Several females to each male spreads the attention so no single female is followed all day, and a group of six or more gives the shoal enough presence that everyone behaves naturally, including the brief, harmless sparring between males.
What group size and layout bring out the best of it
A lone Endler or a pair kept in a bare tank will hide, hug the corners, and show little of the behaviour people keep them for. Give the group numbers, plant cover at the back and sides, and some open water in front, and the shoaling becomes the display: loose streams of small, bright fish crossing the light, regrouping around food, and settling together in the plants as the light fades.
Tankmates should respect the same easygoing pattern. Peaceful fish of similar size let the shoal stay relaxed and visible, while large or nippy companions push Endlers into permanent cover, where their social behaviour disappears even though the fish are still technically together. Numbers change the picture too: a group that looks scattered and restless in a sparsely planted tank of four will often settle into calm, confident shoaling at eight or ten in good cover, simply because there are enough companions in sight at any moment for each fish to feel the group around it. When you add new Endlers to an established group, expect a day of extra chasing and showing off while everyone re-sorts, then a return to the usual loose drift.
When grouping behaviour is a warning sign
A shoal that suddenly packs into one tight, silent cluster and stays there is telling you something has changed: a water quality slip, a new aggressive tankmate, or illness moving through the group. Equally, one fish permanently excluded, hiding alone and not joining feeds, deserves isolation and a close look for injury or sickness. Brief bunching after a fright is normal and passes in minutes; bunching that defines the whole day is not.
Questions like whether a tighter group means stress or simple high spirits are exactly the in-the-moment kind KinsLe's Kinny can help you think through, and what you learn from asking stays alongside your Endler group's profile for next time.