If you show me that other students don't benefit from suitable gifted education, then you'll have an argument. Claiming that treating children with gifted education increases their chance of success is obvious, but misses the point, does it not?
I can specifically remember back to when the TAG Math students (Talented and Gifted) were learning what negative numbers were. I kept hearing about them. I imagined what they might mean, how you use them. When I was finally introduced one year later, I was disappointed, you mean it's literally just subtraction? I could have done that one year ago. And same with all the other students in the normal math course, if they had the same level of attention and care.
The worst part was this: the students in TAG math had a student:teacher ratio of 10:1, while the normal math students had a ratio of 20:1. The remedial students had a ratio of 10:1, but the remedial teacher was from the special ed department, not a specialized math teacher that the TAG and normal students got. The TAG program at my school was praised, and the teacher acted as if she was doing God's work. Of course, she had children who were students at the school, and of course, they were in all of her classes.
Now, looking back on it, I realize how broken this frame of thinking is. Yes, students will benefit if you put them in an elite math course with more resources than other children. Other students will bare the cost. I think a better allocation of our time and money would be to spread resources evenly. If you really want to get ahead by one or two years, take summer classes in middle or high school. That way, the students bares the cost of the additional time and effort, and we can still evenly allocate resources so every eight year old gets the same opportunity.
EDITS: spelling bear -> bare