New York’s top education leaders are gearing up for a spirited fight over teacher evaluations that will likely dominate education policy at end of this legislative session.

The Assembly introduced a bill on Thursday that would overhaul the state’s current evaluation system, which had already been put partially on hold, and prohibit state officials from requiring state test scores in teacher rating systems.

The state’s teachers unions rejoiced at the news, while other education advocates charged that the bill would make it difficult to hold educators accountable — setting up a showdown that lawmakers will have to solve.

The drama surrounding New York’s teacher evaluation system has many characters, including lawmakers, state education department officials, the governor, unions and other advocacy groups. Here’s where they all stand — and why the behind-the-scenes dynamics are so complicated.

Teachers unions could get what they want — but pushback is already forming.

The state and city teachers union are thrilled today. Union members gathering for a meeting in Buffalo this week applauded when the bill was introduced, according to NYSUT spokesman Carl Korn, who called it on Twitter a “Giant step towards protecting kids.” New York State United Teachers President Andy Pallotta said it was “long overdue,” and United Federation of Teachers President Michael Mulgrew chimed in with support, too.

NYSUT has been fighting for immediate changes to teacher evaluations all year and has long argued that teacher rating systems should not place too much emphasis on state test scores.

But there are already signs that their fight will be tough. Besides locking down support from Gov. Andrew Cuomo and the Senate, the union is already facing pushback from education groups. Some advocates warn that a dramatic reversal would move the state backwards, depriving officials of an important way to distinguish whether educators are helping students learn.

Cuomo hasn’t said much — and that might say it all.

No one’s in a more interesting position than Cuomo. If he opposes the legislation, the state’s powerful teachers unions might throw their support to Cynthia Nixon, who’s challenging him for in the Democratic gubernatorial primary — something that he desperately wants to avoid. If he backs the bill he could come off looking like a flip-flopper who let himself get pushed into restoring a patchwork of teacher evaluation rules that he once called “baloney.”

Looming behind the entire saga is the question of what Cuomo, who is seen as a political mastermind, benefits from the ordeal — and if he doesn’t, will he have to swallow this pill for the union’s endorsement or will he let it fall apart in the end?

Republican Assemblyman Edward Ra asked as much on Twitter earlier on Friday. “For some reason no one is asking one obvious question: is the Governor on board on board or I’m gonna veto this in 6 months on board?” Ra tweeted.

So far, Cuomo hasn’t taken a stand. A spokesperson for the governor suggested that he is interested in tackling teacher evaluations this year but did not expressly support or oppose the bill. The governor must have at least some interest in the plan, however, since he’s been participating in discussions behind-the-scenes, according to a statement sent by Assembly Speaker Carl Heastie’s office.

But by not taking a stance immediately, he can avoid a public flip-flop for now and wait and see how the battle plays out among lawmakers.

The Republican-led Senate is a wild card.

While the Assembly is likely to pass its own bill, the Republican-controlled Senate is more of a mystery.

Republican control of the Senate is already precarious. Though Republican Senators are technically outnumbered by Democrats, a single Brooklyn Senator is keeping the GOP in power by conferencing with the opposite party. And the Republicans will be fighting for seats in Long Island, which is the white hot center of the state’s testing boycott movement.

It could be hard for Senators to explain to their constituents that they blocked a bill that reduces the state’s emphasis on testing and you can bet the state’s teachers union, which will be fighting hard for this to pass, will not let them forget it come election time.

State education officials have stayed quiet — and gotten the blame anyway.

We’ve heard little from the state education department, but officials there could well be frustrated. They laid out a timeline for improving the teacher evaluation system by 2019, which coincides with the end of the moratorium on the use of certain state test scores in teacher evaluations. Now this legislation may circumvent that plan.

Plus, Cuomo staffers are actively blaming state education officials for creating the current education crisis in the first place — when in fact the department has been charged with executing on a law that Cuomo spearheaded in 2015. (Cuomo officials say the state education department botched the roll-out of of the Common Core learning standards, leading to much of the dissatisfaction among parents and educators.)

State education department officials said they do not comment on pending legislation but that their process to revamp teacher evaluations has already begun.

Nixon made the first move — and potential supporters were not thrilled.

Nixon, who is challenging Cuomo for the Democratic gubernatorial nomination, offered the first indication that something was brewing in Albany on Thursday morning, when she announced that she would push for a repeal of the state’s evaluation rules.

It looked like an obvious choice as she seeks to win over the state’s teachers unions, but by the afternoon, the unions were criticizing her for jumping into a fight where she wasn’t invited.

“Ms. Nixon’s 11th hour public statement on the bill — while it may score political points — won’t help it get enacted,” UFT President Michael Mulgrew said in a statement.

On Friday, however, Nixon tried to drum up support from union members at a state teachers union meeting. Though she had not been expressly invited, according to Ryan Whalen, a Capitol Tonight reporter, on Twitter, she took pictures with members and tweeted that they should be “treasured and lifted up” for the work they do.

This story has been updated to include information from state education department officials.