Hoping to build on state-level reforms aimed at closing the education achievement gap, the Education Department opened its Race to the Top competition to school districts on Sunday, inviting the poorest districts across the country to vie for almost $400 million in grants.

Following four months of public comment on a draft proposal, the Education Department unveiled its final criteria for the district-level competition, which will award 15 to 25 grants to districts that have at least 2,000 students and 40 percent or more who qualify for free or reduced-cost lunches — a key poverty indicator.

Grants will range from $5 million to $40 million, depending on the size of the district.

"We want to help schools become engines of innovation through personalized learning so that every child in America can receive the world-class public education they deserve," Education Secretary Arne Duncan said in a statement.