Boyle, who represents a district in Northeast Philly and is married to a Montgomery County public-school teacher, touted his record of pushing for more public-education funding but said he "absolutely" supports vouchers.
"Frankly, I think it's a little hypocritical for those who sit on the Main Line and send their kids to wealthy private schools to deny the same opportunity to the urban poor," said Boyle, the father of a newborn daughter.
Leach and the third candidate, Dr. Valerie A. Arkoosh, both live in Montgomery County and send their children to private schools.
Leach, who lives in Wayne - most of which is in Delaware County - said he didn't understand Boyle's "hostility" toward the Main Line and objected to his children being a campaign issue.
Leach said he proudly opposed a state voucher bill designed, he claimed, to funnel public money to Catholic schools.
Arkoosh, who lives in Springfield Township, said she opposes any program that takes money from public schools for private-school tuition but could support a "separate budget item" that provided school vouchers through a different funding source.
Democrats hold a voter-registration edge of 60 percent in the 13th District, half of which is in Montgomery County and half in Northeast Philly. Republicans make up 28 percent of the district; independents and third-party voters account for 12 percent.
The three candidates agreed on several issues: They want the minimum wage raised, they want jobs created through government-funded infrastructure projects, they support the Affordable Care Act, they want more congressional oversight and transparency for the National Security Agency, they want to hold off on more sanctions against Iran until negotiations with that country about nuclear issues have had a chance to proceed.
And they oppose raising the Social Security retirement age or cutting back on benefits.
Margolies, in a meeting Dec. 5 with Montgomery County's Democracy for America chapter, said that "everything has to be on the table" with Social Security reform, opening the door to changes in retirement age or benefits.
"In 1994, there were two folks who were pushing this plan to raise the retirement age to 70," Boyle said. "One was Mrs. Margolies. The other was Rick Santorum."
The mere mention of Santorum's name caused some in the audience to gasp or cry out.
Margolies held the 13th District seat for one two-year term from 1993 to 1995. Santorum was a U.S. House member then, running for election to the U.S. Senate.
Ken Smukler, a senior adviser to Margolies, returned fire later by claiming Boyle has "far more fundamental similarities" with Santorum because both have "taken positions opposing a woman's right to choose" an abortion.
A spokesman for Boyle later responded by saying that Boyle supports abortion rights.
Margolies will not participate in any candidate forums or debates until March 12, the deadline to file nominating petitions to get on the ballot, her campaign said.
Instead of attending the forum in Upper Dublin Township, she appeared on MSNBC yesterday, speaking about women in politics.
On Twitter: @ChrisBrennanDN