What makes teachers grin, but environmentalists grimace? Answer: a campaign to send hundreds of thousands of thank-you cards praising teachers. The Committee on Home-School Co-operation has distributed about 600,000 cards - the equivalent of about 150 trees - to parents this year, urging them to send the cards to their children's teachers. The cards are distributed through schools and parent-teacher associations to encourage displays of parental gratitude. The number of cards sent out this year is six times more than last year's tally of 100,000. About 45,000 cards were sent in 1995. The sacks of cards distributed this year allow 12 cards for each of the territory's 48,000 kindergarten, primary and secondary school teachers. Conservation Association general secretary Lister Cheung Lai-ping suggested parents could thank teachers without culling an orchard of trees. 'Some 9,000 kilograms of paper will be required to produce 600,000 cards. It means 150 trees have to be chopped down. This is not a small number and the figure may be underestimated,' Ms Cheung said. 'I don't mean that people should not send cards, but is it the best method to communicate? And the cards are not designed by themselves or by their children.' Many companies and organisations still printed and delivered masses of cards without a thought for the environment, Ms Cheung said. The 'Parents Also Appreciate Teachers' Drive' is in its third year, and the organising committee said it would keep distributing cards to encourage 'communication between teachers and parents'. A ceremony was held yesterday to present souvenirs to schools which received the greatest number of cards. Ng Yuen Hau-sheung, the mother of a Primary Three girl, admitted some parents did not realise the meaning of the cards and simply filled them in as a matter of routine. Teacher Chan Lai-hing said she was pleased to receive more than 30 cards from parents, although she had yet to read them all.