On Thursday, the Minnesota House was supposed to vote on a bill that proposes revamping the school system's teacher tenure rules.

But it didn't happen.

Instead, after what Northland's NewsCenter describes as a "heated, but short-lived debate," that proposal was sent back to the House committee where it came from.

What's the debate about, and why did the bill get sent back? Here's an explanation.

The bill

The proposal focuses on the way teachers in Minnesota get tenure, which right now is based mainly on seniority. (The Star Tribune goes into exactly how it works, so give that a read for more.)

There's a lot to the bill, including new guidelines for hiring out-of-state teachers and clarifications on exams that gauge a teacher's skill.

But the headliner is a revamp of teacher tenure, that would eliminate the "last in, first out" policy and emphasize the quality of teaching over time on the job, MPR reports.

The bill was introduced by Republican Rep. Jennifer Loon, of Eden Prairie. (Click here to read the full bill.)

Rep. @JeniferLoon & education advocates discuss HF2 which improves learning & empowers teachers & schools. #mnlegpic.twitter.com/Diklyvv04U

— MN House Republicans (@mnhousegop) February 26, 2015

Why is this a focus?

"Last in first out" policies are under fire in a number of states.

Proponents say it offers job stability to committed teachers, and is a clean way to go about layoffs. Opponents however say it prioritizes teachers over students, and doesn't ensure kids get the best educator possible.

The Star Tribune dug into some education department data, and found 2,200 teachers were laid off under the LIFO policy from 2008-2013. A separate look at teacher contracts showed local districts' contracts rarely outlined performance as a reason for firing, and instead looked at seniority.

Many Republicans support the bill, but it's expected to be a tough sell for DFL lawmakers and Gov. Mark Dayton.

Why didn't the House vote yesterday?

One of the biggest opponents of this bill is Education Minnesota, the state's largest teachers' union. (If the bill made it into law, many of the current rules they've fought for would be altered or eliminated.)

On Thursday, the union put out a statement saying the cost of any of the proposed changes was unknown, and voting on the bill before getting those numbers is "reckless."

But the Management and Budget Office, just hours later, said the new rules would cost $895,000 over the next two years, according to MPR. That information came out right before the House was supposed to vote, with some Republicans questioning the timing.

So the House voted to send the bill back to the Ways and Means Committee – it could be brought back up for a full House vote next week.