Returning their used cutlery after every meal in the school canteen is something students do without question ("No reason not to return your trays at this food centre"; July 4).

This is so because it is expected of every student. Younger students see their older schoolmates doing so, and will follow suit.

However, when students grow up, this practice of returning trays or cutlery ceases. One reason is that they do not see others doing it in public eateries, and there are always cleaners to clear the tables after them.

A public campaign to urge Singaporeans to return their trays, like on the scale of the Speak Mandarin and past courtesy campaigns, may work.

This campaign should target schools so students can act as reminders to their parents to return their used cutlery or trays at public eating places.

Such campaigns can capitalise on the herd mentality - when a person sees others returning the trays, he will tend to follow suit.

Clara Chua Sieo Peng (Ms)