Ms Priscilla Poh Beng Hoon (Good sleep routine ensures children's body clocks are set; March 3) and Mr Seah Yam Meng (Push back start time of schools for health's sake; ST Online, Feb 24) are both right to state that sleep is important for health, cognition and well-being, and to offer support for improving students' sleep.

I acknowledge that changing the start time for all schools may be challenging, due to transport arrangements.

Hence, I suggest confining this change to secondary schools.

Students at this age may be more suited for ride-sharing or public transport schemes.

My group also recently gathered our own data on students' sleep patterns and found that there is a systematic decrease in sleep duration in mid-secondary school.

This is a result of a biological shift in preferred sleep time to later in the night.

Advising older teens to go to bed earlier, to achieve more sleep, is unlikely to be effective on its own.

My colleague, Dr Joshua Gooley, also found that students who attend secondary schools here that start later get more sleep on school nights.

Hence, changing the start time for secondary schools could benefit the age window where sleeping later is biologically driven, and could encourage further adjustment to sleep schedules.

Michael W. L. Chee (Dr)