Gov. Charlie Baker reignited a debate on Thursday that has vexed and divided Democrat and Republican lawmakers in recent years, proposing an expansion of charter schools that would be targeted toward the lowest performing districts statewide.

Baker chose the Brooke Charter School in Mattapan, in the district of Education Committee Co-Chair Sen. Sonia Chang-Diaz, to lay out a case and proposed path forward to expand and more closely align charter schools with traditional public school districts.

Baker's pitch, and the expected push from the administration to get the Legislature to act by next summer, makes good on a campaign promise to fight for a charter school expansion in the face of critics both on and off Beacon Hill who argue that charters siphon important financial resources away from traditional public schools.

"As I stand here today, there are 37,000 kids who want to get in to a charter school, 37,000 families who simply want...something bigger and better for their children," Baker said, later indicating that he could be willing to negotiate with legislative opponents over the funding issues that doomed a bill in the Senate last year.

Both major teachers unions, the Massachusetts Teachers Association and the American Federation of Teachers, immediately ripped the proposal, offering a taste of what the governor can expect from opponents of charter schools over the coming months. MTA President Barbara Madeloni said the plan would "severely undermine" the state's public education system.

"His plan would accelerate the dangerous direction in which we are already headed: toward being a state with a two-tiered education system, one truly public and the other private, but financed with public dollars," Madeloni said in a statement. "The truly public system will always welcome all students. The private system will continue to find ways to underserve those with the most needs and then use inflated claims of success to grab an ever-larger share of public education funding."

The governor's bill, which he is expected to file with the House later Thursday, would allow the state to license up to 12 charter schools statewide, above existing caps, in districts that perform among the lowest 25 percent in the state, or about 70 districts.

While that section of the governor's bill is "basically the same" as what advocates have proposed in their petition for a 2016 ballot question, Baker's bill goes further to allow charters to give added weight in lotteries for seats for seats that would give added weight to low-income students, English language learners and other "high needs" students.

"This is intended to ensure charters are going the extra mile to enroll as many high-need students as possible," Education Secretary Jim Peyser told the News Service.

Another provision would allow districts to partner with charter operators to help rehabilitate low-performing schools before they enter Level 5 status and are put at risk of a state takeover. The bill would also permit charter schools to reach agreements with local districts to participate in district-wide enrollment systems based on parent preference, similar to what has been proposed in Boston.

Despite the attempt to encourage charter schools to serve more high-need students, Madeloni said charters tend to lose a significant numbers of students with English language and special education needs who can't meet their "disciplinary demands or whose academic and social needs are significant."

Baker, citing his previous work on the board of the Phoenix Academy Charter Network, said he rejected the notion that charters skim the best students from the pool, leaving traditional public schools to educate students in need of more services and attention.

"A lottery is a lottery. It's a game of chance, and one of the things that bothers me the most about the cap is you take parents and kids and you put them into a game of chance in which the vast majority are going to lose. We have to be able to do better than that," Baker said.

Dozens of students from the Brooke Charter School joined the governor, holding signs that read, "Lift the cap" in both English and Spanish.

The Education Committee plans to hold a hearing next Tuesday on charter school bills, including Baker's proposal. Baker told reporters he personally planned to testify before the committee.

Chang-Diaz, whose concerns over expanding the charter cap last session led to the House acting on a bill without the blessing of the Education Committee, said she's trying to keep an open mind as the debate ramps up again.

"I think this is the very first step in a process, so I'm going to read the bill first, but I hope you will take this as genuine and at face value, I sincerely am going to work with all comers who are genuinely committed to doing justice for kids who are underserved in whatever setting they exist in," the senator said.

Last year, the House's bill to partially lift the charter school cap ultimately failed in the Senate, dooming the issue for the session. Funding that follows students to charter schools, and the impact that has on cash-strapped school districts, became a major point of contention in the 2014 Senate debate over expansion.

"I'm perfectly happy to have a conversation about the funding formula if they want to have a conversation about that," Baker said on Thursday. "But we should all remember that the kids that are served in public charter schools live in the same communities and same neighborhoods as kids that go to traditional public schools and the traditional public schools and the charter schools are both being paid for through a combination of state and local funding."

For children who still might like to enroll in a charter school but do not get picked in a lottery, Baker said his administration has been "pretty aggressive" about increasing Chapter 70 school aid and is in the process of evaluating new standards as part its review of the PARCC standardized test.

Senate President Stanley Rosenberg said he has planned three caucuses for members to hear from proponents and opponents of charter school expansion as the Senate begins a "deep dive" into all legislation related to charter schools. The first caucus - which took place on Wednesday - included officials from the Massachusetts Charter Public School Association, the Neighborhood House Charter School, Phoenix Charter Academy and Brooke Charter Schools.

The next caucus on charters is tentatively scheduled for next week.

Rep. Alice Peisch, the House co-chair of the Education Committee who helped push a charter bill through the House last session, told the News Service the governor's bill would "go through the same process" as any other bill.

Along with bills before the Legislature, proponents of increasing access to charter schools have filed a lawsuit and are in the process of bringing a ballot question to voters. Critics of charter schools say they subvert the local governance of school committees and sap resources from local school districts.

Peisch said she would "prefer" that changes to charter school laws take place through the Legislature and she is "cautiously optimistic" that will be the case.

Asked if she felt added pressure this session due to the threat of the ballot question moving forward in the absence of legislation, Chang-Diaz said she too would prefer a legislative solution.

"For me the driving pressures that I feel are one to do right for my constituents in my district and two, to try to midwife a good system into being that works for the state as a whole. Those are plenty pressures enough, so I don't need additional motivation, but the ballot initiative process, whether it's in education or in other policy, I have always felt is a very blunt tool, so if we can do it better with more precise instruments in the Legislature I would certainly prefer that," Chang-Diaz said.

Boston Foundation President Paul Grogan called Baker's proposal a "sober, pragmatic, gradual approach," and said he's excited to see a governor elevate the issue of access to charter schools to the top of his priority list.

Grogan, who named new Boston Superintendent Tommy Chang as an example of the "ideal" administrator to translate more of the successes in charter schools into programs at district schools, said expanding charter schools will help set more examples for how other public schools can succeed.

"I think there will be a convergence," he said.

A coalition of parents and educators called the Massachusetts Education Justice Alliance joined the chorus uniting against Baker's bill.

"The Governor's bill would divert more and more money from our public schools to charters that aren't accountable to their local communities, and it would do nothing to address the high suspension rates that charter schools use to educate fewer students with special needs, students who are learning English, and students from economically disadvantaged areas," said Russ Davis, of Massachusetts Jobs With Justice.

Andy Metzger contributed reporting.