Not all who got written test will got interview. Only those shortlisted. Just simply chit chat during interview but not sure whether all interviewed will got admitted.
My son is studying at a government aided school. It's pretty well taken regionally but it's not teaching faster like most private schools.
My son ranks first in form for the year. He is not particularly strong in sports. He has got a few certificates but they are the ordinary ones like Cambridge English Test & Speech Festival.
My wild guess is that the crucial part is passing the entrance exam. But I really don't know.