Possible Clues:

• Can't a teacher somehow put across central bit of information — where pupils are coming from?
• Region from which a river draws rain
• Area from which rainfall flows into a river
• A teacher can't initially make out where pupils come from
• Fish workers on old boat - each with an allotted space
• Region from which a school's pupils are drawn
• A chance matter, relocating to this locality
• River drainage basin
• Hear name broadcast about plant? It's served by an institution
• Terrain from which a river is fed