To fall behind or drop out (e.g., in a class or group because of poor performance or slow progress).
勉強についていけず、クラスで落ちこぼれる生徒が増えている。
The number of students who fall behind in class because they can't keep up is increasing.
進度が速くて、何人かは授業についていけず落ちこぼれた。
The pace was fast, and several students couldn't keep up and fell behind.
支援がなければ、才能があっても落ちこぼれることがある。
Without support, even those with ability can end up falling behind.
To drop, spill, or scatter — used for things that fall out and scatter (e.g., contents spilling from a bag).
袋を落としたら中の豆が道に落ちこぼれた。
When I dropped the bag, the beans inside spilled out onto the road.
棚の隙間から小さな部品が落ちこぼれて見つからない。
Small parts fell through the gap in the shelf and can't be found.