Approach whichever school you want.
Get the application forms.
Sit for the appropriate aptitude tests. Get ready the money for the
next few years of lessons, pubbing, school tours, parties, discos
etc. I've heard that they had problems with drugs and guns. Maybe
govt schools too, i don't know. But you might need to prepare bail
money and lawyer fees just in case you get framed or
something.
Of course Singaporeans can apply for international schools. Most of
these schools have school terms like that of Europe and China ie
they have summer holidays much longer than in Singapore. Then most
of your school mates will return to their home country for summer
hols.
Besides the usual expats' brat attitudes, I heard some have very
good teachers. SAS if I'm not wrong has one economics teacher who
was a Havard graduate, teaching junior high school (secondary/jc)
level.
LHL's eldest son was in one of the international schools too. Not
sure if still there.