one day got 24 hours right
lets observe the average life of a sec 4
so.. if lets say school starts at 7.20
and EVERY student has lessons till 4... or sometimes 4.30
just to be optimistic, lets say the teacher miraculously ended on time and
the students off at 4.

thats alr 9hrs of the day gone.
most students take at LEAST one hour to reach home. which will be 5pm.
on reaching home, the basic neccessities of a human are to eat dinner and bathe..
make it 1 hr. it will be 6pm by the time the student finishes dinner and bathing.

so.. on to homework. they get loads everday.
so it definitely takes more than one hour to finish homework
lets make it 2hrs. so by the time its done it will be 8pm. damn.

so, he/she gets ready for the next day and goes to sleep at approx...........  9pm?
the average student wakes up at 5 to eat breakfast and get ready
so
the number of hours he gets to sleep is 8. which is the so called healthy sleep level

BUT
there are many things i havent counted
wad about stuff like
1)CCA
2)Occasional traffic jam
3)The teacher release late ( happens very often )
4)Recreational Time eg TV/Computer and all that
5) many more..
but with these four factors alone,
it can be easily predicted that the average sec 4 student gets much less than 8 hrs sleep

so,
issit right to say that
all Secondary 4 students are unhealthy?

ps. other schools have to stay back way after 4.
& cca can delay till 6plus or much much later.