UPDATED

Hear that collective whoop from the Capitol? That’s the sound of education advocates and lawmakers cheering at the finish line as the first rewrite of the Elementary and Secondary Education Act in more than a dozen years sails through Congress and on to the White House.

The U.S. Senate on Wednesday approved the rewrite of the withering No Child Left Behind Act—the current version of the ESEA—by a huge bipartisan margin, 85 to 12, mirroring the vote of 359 to 64 in the U.S. House of Representatives just days earlier. President Barack Obama is expected to sign the bill Thursday.

But even as educators and policymakers toast the passage of the Every Student Succeeds Act, the next set of battles—over how the measure will be regulated in Washington and implemented in states—may just be getting started.

The bill, sponsored by Sens. Lamar Alexander, R-Tenn., and Patty Murray, D-Wash., and Reps. John Kline, R-Minn., and Bobby Scott, D-Va., would roll back the federal footprint in K-12 education for the first time in nearly a quarter century, putting states in the driver’s seat when it comes to accountability, teacher evaluation, school turnarounds, and more.

At the same time, it seeks to maintain what Murray and Scott call important “guardrails” to fix flailing schools and help close the achievement gap between traditionally overlooked groups of students—those in poverty, racial minorities, students in special education, and English-language learners—and their peers. (Everything you ever wanted to know about the bill here.)

And ESSA slims down the U.S. Department of Education—consolidating nearly 50 programs into a giant block grant—and aims to crack down on the U.S. Secretary of Education’s authority when it comes to standards, assessments, school turnarounds, teacher evaluation, and other areas.

It’s an open question how the prohibitions on the secretary’s power will square with the bill’s accountability requirements. Scott said last week he’s confident the secretary of education will have enough power to enforce the new law.

But some policy analysts still see plenty of ambiguity and unanswered questions. (More on that below.)

Gearing Up For Implementation

More important even than the regulatory process in Washington, though, may be the work that goes on in statehouses across the country over the next year as implementation begins.

Under ESSA, states will get to decide whether to stick with teacher evaluations through student outcomes (in place in 42 states and the District of Columbia) and the common-core standards in place in more than 40 states. The Obama administration pushed both those policies—plus aggressive school turnarounds—under its waivers from the NCLB law.

And, even though ESSA would maintain annual tests, states could dial back the role those assessments play in school ratings and accountability, in favor of other factors, like school climate, teacher engagement, and access to advanced coursework.

The changes to teacher evaluation and the potential rollback of testing’s importance have Lily Eskelsen Garcia, the president of the 3 million member National Education Association, pretty excited. (See who else supports the bill here.)

“We will see the end of test and punish,” she said in an interview Tuesday. “We will see the end of hit your cut score or somebody gets punished.”

Despite claims that Congress is broken, NEA was able to work with a “really thoughtful group” of lawmakers to get many of the changes to ESEA it had been seeking for years, Eskelsen Garcia said.

The next task? Helping state affiliates pull off the same thing. “If we can do that in Congress, our counterparts on the state level have some hope of doing something with even a hostile legislature,” she said.

Teachers’ unions aren’t the only ones who see ESSA as an opportunity to influence the direction of state and local systems going forward.

The Leadership Conference on Civil and Human Rights, which offered a measured endorsement of the bill, is taking seriously language calling for broad community engagement in developing state and district plans to implement the law.

“This [bill] provides leverage about what needs to be done differently, but it is not the end all and be all. It is a framework,” said Liz King, the conference’s director of education policy Tuesday.

The civil rights community can help local advocates work with districts, states, and educators to make sure traditionally overlooked students get access to their fair share of resources, and that accountability plans call for district and state supports to kick in when they are falling behind, King said.

Of course, there will be work to do inside Washington as well, King said. “On the accountability side, we’re going to be there at the table on the development of regulation, helping partner [organizations] understand where they can be engaged.”

UPDATE: Two GOP presidential candidates, Sens. Rand Paul of Kentucky and Ted Cruz, opposed the bill’s passage. (Cruz put out a statement, Paul voted against it.) Sen. Bernie Sanders, who is running for the Democratic nomination, missed the vote, as did Sen. Marco Rubio of Florida, a Republican candidate. Hillary Clinton, the Democratic front-runner, gave the bill a thumbs up, and even said something nice about its provisions for charter schools.

Regulatory Head-Scratchers

The regulatory process, slated to kick off in coming months, could call for the department to puzzle through some wonky head-scratchers—with potentially serious implications for the future of accountability, one former education department staffer said.

“The bill leaves a lot of gray, murky areas and uses some words that are open to interpretation,” said Chad Aldeman, now an associate partner at Bellwether Education Partners. “Depending on what the secretary tries to do, I think it could open him up to lawsuits.”

Case in point: In what could be a win for the civil rights community, ESSA calls for states and districts to flag, and help fix, schools where traditionally overlooked groups of students are “consistently underperforming.” But what, exactly, does that phrase mean? And do states get to define it, or does the Education Department?

Questions like that could be complicated by the bill’s lengthy laundry list of prohibitions on the secretary’s authority. That language is largely seen as a rebuke to Duncan, who Republicans say overstepped the bounds of his office big time in issuing conditional waivers (aka flexibility from NCLB in exchange for certain policy promises).

Duncan, who gave a sunny speech on the bill Tuesday, is stepping down this month, leaving John B. King Jr., the former New York commissioner, as acting secretary. King will put the Obama administration’s final stamp on the law.

But ESSA won’t be fully in place until the 2017-18 school year, which could leave a lot of the work of monitoring and implementation to the next administration.

Bipartisan Balancing Act

For his part, Alexander, who championed the provisions clamping down on the education department, doesn’t think there’s room for the agency to overstep its bounds.

“This bill specifically prohibits the secretary from issuing regulations that aren’t authorized by law. That’s in there several times,” he said in a quick interview Tuesday. And he isn’t expecting a stormy implementation process. Instead, he said, it will likely build on the law’s bipartisan support in Congress—and be largely handled in states and districts.

When it comes to school turnarounds, standards, and teacher evaluation, “school districts and states can immediately make those decisions again without having to come to Washington and play ‘Mother May I’ and ask the U.S. Secretary for permission,” Alexander said.

And Murray sees ESSA as hitting a particular sweet spot: It’s meant to get away from the “one-size-fits-all” nature of NCLB, without stepping back from of the law’s focus on protecting vulnerable kids. States and districts will still have to set high expectations for all children and put in place “evidence-based” interventions when schools need them, she said in a quick interview Tuesday.

She’ll be watching closely to make sure the legislation’s balance is maintained, she added.

“Passing a bill is not the end of your job here,” Murray said.

Sen. Patty Murray, D-Wash., center, joined by Senate Minority Leader Harry Reid, D-Nev., right, and Sen. Chuck Schumer, D-N.Y., speaks to reporters Tuesday after the Senate voted overwhelmingly to end debate on the makeover of the No Child Left Behind Act, setting up a final vote on the legislation on Wednesday. Murray was a chief architect of the bill along with Sen. Lamar Alexander, R-Tenn. --J. Scott Applewhite/AP