The way our school, which probably has similar demographics to yours (about 60% economically disadvantaged, about 70% English language learners) but is not failing anymore, does it is to cluster all "high" kids (defined starting in 3rd as those who got an "advanced" on state tests the previous year) and have them work on the next grade curriculum, at the cost of a lower teacher:student ration.
Kids at or below grade level, which by this point is a relatively smaller group, work on grade level materials with a higher teacher:student ratio.
This seems to give good results (more than half the students are in the advanced group in 3rd grade this year) while keeping most people happy (high performers get more challenge, low performers get more resources).
