Schools are to be told how heavy their students' textbooks are. The aim is for classes to be scheduled so that children do not have to carry too many at once. For the first time, the Education Department has demanded publishers display the weights of their books for kindergarten, primary and secondary school students for the new academic year. The department has added the information to its recommended book lists for schools. It is hoped the list will help schools choose textbooks and arrange a better timetable to prevent students overloading backpacks. There has been concern for years over damage done to children's backs by heavy bags. Doctors have suggested students should not carry a bag weighing more than 10 per cent of their own body weight or the development of their spine could be affected. The Consumer Council found early this year that 90 per cent of primary and 70 per cent of secondary students were overloaded. A Primary Five boy was found to be carrying a school bag weighing more than seven kilograms - nearly a third of his body weight. The department's principal curriculum planning officer, Cheng Sai-man, said almost all textbooks had their weights listed. 'Schools of course should choose books for their students according to their contents and quality instead of their weight,' said Mr Cheng. 'But the weight list will help teachers figure out how heavy their students' school bags could be that day. 'They can also arrange a better timetable and avoid asking students to bring too much stuff to school on a day with lessons with too many heavy books.' According to the new list, the weight of textbooks ranges from 60 grams to 900 grams. Economics Today by Jing Kung Educational Press for Form Four and Five students, for instance, weighs 700 grams. The Longman English Express published by Longman for Form Four and Five students is 600 grams, and Mathematics for Hong Kong by Canotta Publishing Company for Form Three students weighs in at 900 grams. Chairman of the Hong Kong Subsidised Secondary Schools Council Stephen Hui Chun-yim welcomed the weight list but feared publishers would split books into two or three sets, and parents may need to pay more for books.