Colorado senators gave initial support to a bill that would require the state’s school districts to equally share voter-approved tax increases with their charter schools, but not before making substantial changes that would ease in the new mandate.

The bipartisan approval came after two days of intense debate that rehashed longstanding arguments over the role of charter schools.

The local tax increases, known as mill levy overrides, have become a popular way to supplement school districts’ budgets as the state has not made headway in closing a $830 million school funding shortfall. These tax increases may only be used to fund specific programs, such as full-day kindergarten.

Under current law, school boards must consider the needs of their charter schools, but are not required to share any of the new revenue. Charter schools receive state tax dollars but are run independently, outside of the traditional school district system.

The bill would apply to all previously approved tax increases, and those going forward.

Districts won’t be obligated to back pay charters retroactively. But going forward, school districts would be required to send a combined $33 million to their charter schools to make up current inequities, according to a legislative estimate.

Districts will only be required to share tax dollars if charter schools offer comparable programs voters approved funding for.

But districts wouldn’t need to share all that money at once. An amendment to the bill would allow districts to phase in the new sharing requirement.

Under a second amendment, school boards could ask voters this fall — and only this fall — for approval to keep the status quo from previously approved tax increases, meaning charters would not get an equal share if they didn’t have one earlier.

Democrats who opposed the bill proposed 10 amendments that were inspired in part by longstanding criticism of charter schools.

Failed amendments included one that would have limited sharing money with only those charter schools that serve an equal percentage of students with disabilities as their authorizing district. Another failed amendment would have forbid sharing with charters that operate under one of the 17 automatic waivers from state law — effectively neutering the bill.

During debate, supporters of the legislation framed the push to equalize funding as an equity issue. According to a recent report by the state education department, charter schools in Colorado are increasingly serving an at-risk student population.

“These kids are receiving unequal funding and they’re disadvantaged from the point they walk into the classroom,” said state Sen. Angela Williams, a Denver Democrat and one of the bill’s sponsors. “It’s about ensuring students of color, undeserved students and students with disabilities have equal funding.”

The bill falls short in equalizing funding for all charter schools. Earlier, the Senate Appropriations Committee striked the requirement that the legislature send $17 million to charter schools authorized by the state through the Charter School Institute.

Opponents of the bill argued that local school boards are best positioned to decide how to spend local tax revenue.

“I trust the parents, I trust the teachers, I trust the administrators to do the right thing and do what’s best for all of our children,” said Don Coram, a Montrose Republican.

The Senate is expected to hold a final vote on the bill Tuesday. Then the state House will take up the matter. A similar bill died in that chamber last year, and some Capitol observers expect this bill will suffer the same fate.

Update: This post has been updated to clarify that voters approve funding for specific programs when they vote for mill levy overrides, and that districts will only be required to share tax dollars with charters with comparable programs. This post has also been updated to clarify that the bill applies to past and present mill levies, but districts aren’t required to retroactively pay charters.