The Senate bill echoes legislation unanimously passed by the State House in October, part of a multi-year effort in Massachusetts to overhaul reading instruction methods.

Senator Sal DiDomenico, the Senate leader on the legislation, said the bill is vital to ensure the state’s high educational achievement applies to all groups.

“We rest on our laurels a lot about being #1 in education across the nation, but when you dig a little deeper, it’s a tale of two cities,” DiDomenico said. “Only four out of 10 third-graders are reaching benchmarks at reading.”

The numbers are worse for subgroups such as Black students, low income students, and English learners, DiDomenico noted. Just 14 percent of students with disabilities, for example, are meeting benchmarks, he said.

The bill has the backing of Governor Maura Healey and Senate President Karen Spilka, alongside a coalition of groups known as Mass Reads that includes education reform-linked groups like charter schools, civil rights groups like the Boston branch of the NAACP, and business groups. (A number of the members of MassReads have received grants from the Barr Foundation, which also helps fund the Globe’s Great Divide education reporting team.)

The bill faces opposition from some organizations, however, including the state’s largest teacher’s union and an education professor whose curriculum could be prohibited in Massachusetts schools.

The Senate proposal diverges most notably from the House by requiring the Department of Elementary and Secondary Education to provide a complete kindergarten-to-Grade 3 curriculum for free to schools. That provision could in part address the concerns of local district that the legislation is a unfunded mandate on local governments.

The Senate plan also eliminates a ban, which the House bill included, on “three-cueing,” a widely disparaged technique that involves using context like pictures instead of phonics to figure out unfamiliar words.

If the bill passes, the House and Senate will need settle any differences before sending the legislation to Healey for her signature. In a statement, the governor praised the bill.

“We have been proud to partner with the Legislature to increase literacy funding, and this bill is another important step toward ensuring every student has high-quality literacy education,” she said.

The Senate will address dozens of proposed amendments to the bill before voting Thursday, including one that would largely defang it by removing the requirement that all curriculums get state approval. Others would increase the state’s responsibility to cover costs, along with various proposals not directly related to reading.

As part of its bill, the House passed a union-backed set of amendments centered around promoting librarians, reading specialists, and other school-based literacy staff. Similar amendments are also before the Senate.

Similar bills have failed in the Legislature for years in the face of opposition from the Massachusetts Teachers Association and some local school districts. Critics have decried proposals as restricting teachers’ autonomy to adapt to student needs and disputed the validity of the “Science of Reading” movement, a body of research in part underlying the bills that emphasizes phonics as a key to early reading success.

“Curriculum mandates are an oversimplified response to a complex problem,” said Max Page, president of the union, in a statement. “There is no proof that such mandates yield sustained success in any of the states that have passed so-called literacy laws.”

The legislation has drawn less coordinated opposition than it did in some prior years. The Massachusetts Association of School Superintendents opposed similar legislation in 2024, for example, but has largely sat out the current battle.

Supporters argue a mandate is needed to stop districts from using curriculums the state considers low-quality, a widespread practice covered by the Globe’s Great Divide education team in a 2023 investigation. Mary Tamer, the founder and executive director of MassPotential, a Boston-based education advocacy organization that is part of the MassReads coalition, said teachers will benefit from the curriculum requirement.

“We know, having followed what other states have done, the tremendous difference it can be make when a district is not only using the proper instructional materials but when teachers are trained in the use of those materials,” Tamer said. “We want to make sure every principal, every teacher has access to high-quality instructional materials.”

Most states have passed some sort of “Science of Reading” law in the last few years, many with limited results. But proponents of the Massachusetts bill point to states like Louisiana and Mississippi, which have bucked the nationwide decline in achievement over the past decade in part via comprehensive reading instruction reforms.

Both sides agree that much will depend on the bill’s implementation. The state-provided curriculum, for example, could come in any number of forms: The state could expand its existing Appleseeds literacy materials, which currently cover only Kindergarten to Grade 2; it could develop something new; or it could license and adapt other existing materials, such as the free University of Florida Literacy Institute Foundations Toolbox.

One of the biggest concerns from critics has been cost, with the union opponents arguing that the proposals to date do not go far enough in paying for the transition. The Senate bill would create a new special fund, seeded with $25 million in Millionaires’ Tax funds, which the state’s education department could use to develop or adapt the free curriculum, and provide grants to districts to help them implement the law.

Healey and the state Legislature have already provided tens of millions of dollars in funding for curriculum improvements, teacher training, and tutoring over the last few years. In her 2027 budget proposal released on Wednesday, Healey proposed further increasing that investment.

Similarly, the state already publishes a list of curriculums it considers high-quality, based on reviews by Massachusetts teachers and by groups such as EdReports, a North Carolina-based nonprofit that evaluates teaching materials. But that list could grow or change in the future, particularly as new curricula are published in response to similar laws across the nation.

Both bills allow districts to seek waivers from the state list by demonstrating their curriculums align with the law’s definition of evidence-based instruction. Several amendments before the Senate would expand waivers to cover districts or schools that prove they have strong reading results, regardless of curriculum.

“At the very least, let the schools and districts that are doing really well off the hook,” said Lynn Schade, a former teacher and teacher training provider who opposes the bill. “If it ain’t broken, don’t fix it.”

Christopher Huffaker can be reached at christopher.huffaker@globe.com. Follow him @huffakingit.