Gov. Bill Lee's signature education savings account proposal could be pared back to just two counties when it goes back before the Senate next week.

Lt. Gov. Randy McNally, R-Oak Ridge, alluded to those changes on Thursday, which would make it dramatically different than the House bill that advanced this week.

And the Senate speaker conceded that the controversial measure — which would provide money for parents to take their children out of public schools and allow them to spend the funds on private school or other education-related expenses — could be headed to a conference committee.

When asked about the main differences between the House and Senate versions of the bill, McNally told reporters, "I believe the Senate has (ESAs) in Shelby County and Davidson County."

Although it was initially unclear exactly what changes McNally was referring to, his spokesman later confirmed an amendment is being drafted to limit the voucher-style program to schools in the state's two most populous counties.

The most recently approved version of the Senate bill was limited to Tennessee's six lowest-performing school districts and the state-run Achievement School District.

Adam Kleinheider, McNally's spokesman, said an amended version of the bill is being worked on and would likely include the provision to limit it to schools in just Shelby and Davidson counties.

Kleinheider said other components of the forthcoming amendment are still unknown.

The House version of the education savings account bill has been amended four times in as many committees. The Senate version has been amended once, in the only committee where it has been considered.

The current versions of the Senate and House legislation have several differences.

This week, the House changed the bill to provide some type of funding to schools throughout the state, beyond the counties targeted in the ESA proposal.

The Senate version of the bill would allow home-schooled students to participate in the program.

With the different versions between the two chambers, McNally said, "I think that it may end up in a conference committee."

Lawmakers use conference committees to settle disagreements between the House and Senate. The same version of each bill must be approved by both chambers before a measure can head to Lee's desk.

Although the Senate education committee was expected to take up the bill this week, it was delayed, causing some to wonder if the legislation could face opposition from the panel.

Sen. Todd Gardenhire, R-Chattanooga, told the Chattanooga Times Free Press he would not be voting for the ESA bill, despite support for school vouchers in the past.

But McNally remained confident in the bill's ability to succeed in the Senate finance committee and on the chamber's floor.

"I think the votes are there," he said.

The House is scheduled to vote on the proposal Tuesday.

The proposal has faced opposition from civil rights and teacher groups, and superintendents and school boards throughout Tennessee. Advocates of the measure say it is necessary in order to give parents additional choices and encourage failing schools to improve.

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Reach Joel Ebert at jebert@tennessean.com or 615-772-1681 and on Twitter @joelebert29.