If grade school is for socialization than it should be focused on socialization. Group activities, athletic competitions, creative projects, theater performances, etc.
But won't it make it better for everyone else? Not even sure that bottom 5% should be in school. Just train them for a role that they can be competent in or decide that they will be a future ward of the state.
My 6 year old is doing basic algebra and geometric proofs and I worry it's going to make him bored in math class. But even if my kid is a genius it's proven to me that we can be moving our kids much faster than we do. I don't think kids in Singapore have special DNA.