It can narrow the gap & improve children's lives.
I don't think very many people are calling for indiscriminately spending 'more'.
In chicago, what i read is:
1) for whatever reason, some of the money that *is* being spent isn't reaching low-income classrooms (no air-conditioning, books, paper, libraries, music/art classes v. selective enrollment schools which have these things)
2) money is being spent stupidly (more bucks for the head office while teachers are cut, more $ to consultants, testing companies, private education management companies, & other overhead)
Teachers in chicago are asking for spending on:
1) smaller classrooms
2) decent/reliable equipment/supplies/conditions
3) wider curriculum (art/music/libraries etc)
4) social support personnel (nurses/counselors etc)
and an end to spending directed at destabilizing schools.
the relationship between class & educational achievement holds across time & across cultures. however, it's also clear that when well-targeted money is put into closing that gap, it has results (as the us did post ww2 -- the biggest leap in educational achievement in our history -- coincidental with a rise in jobs and wages).