The newly-elected leader of a powerful American teachers’ union has vowed to continue the fight against voucher schemes that was started by her predecessor.

Sally Feldman, speaking just minutes after being elected president of the 940,000-strong American Federation of Teachers by a unanimous vote of its 39-member executive council, said vouchers were “radical schemes that don’t have a shred of evidence to support them”. The vouchers allow low-income parents to send their children to fee-paying schools.

Feldman is the AFT’s first new leader in 23 years after its last leader, Albert Shanker, died of cancer in February.

A former elementary schoolteacher, Feldman, like Shanker, rose through the ranks of the union’s powerful New York organisation. Although she spoke of the need to defend teachers’ pay and maintain high academic standards, she devoted most of her maiden speech to a spirited defence of the virtues of a public education.

The AFT is the second largest US union after the National Education Association, which has 2.2 million educators on its books. But with a membership drawn heavily from big urban school districts and, when headed by the outspoken Shanker, the AFT had a higher profile than its larger rival.

There is speculation that Feldman may struggle to fill Shanker’s shoes, even though she succeeded him as the president of New York’s United Federation of Teachers, where he was her mentor. Shanker was responsible for modernising the AFT and increasing its membership from just 50,000 to nearly a million.

However, Feldman has won praise in New York for pushing for smaller classes and schools, and easing union rules to allow schools more flexibility on promoting and transferring teachers. She has also worked to give teachers a bigger role in decision making.

“Public education was everything to me,” said Feldman, the daughter of a Brooklyn milkman. Teachers knew what they needed to do their jobs well, she said. “Not vouchers. Not privatisation. Certainly not mindless budget cutting. We need high standards, quality teachers, and safe, orderly classrooms,” Feldman told members.

Under Shanker’s leadership, the AFT found some common ground with reformers on charter schools, publicly funded schools that operate semi-independently of school districts, and whose numbers are rapidly growing.

But the AFT’s sharpest clashes with the conservative element have come over voucher schemes, under which parents are given vouchers towards fees at the independent school of their choice.

Feldman, echoing the union’s long-held line, called such schemes “obscene” and said that “idealogues” were exploiting the problems of failing or troubled schools to push vouchers.

The leading national battlefields over vouchers are in Milwaukee, in Wisconsin, and Columbus, Ohio, two cities that introduced limited voucher schemes. In Milwaukee, where vouchers have been on offer for six years, claims that academic results have improved are hotly debated by experts on both sides.

In Columbus, the AFT sued to block a voucher experiment, aimed at 2,000 parents, that began last autumn.

Lawyers for conservative groups entered the case against the union, but last week the AFT claimed a major victory when an Ohio appeal court ruled unanimously that the scheme violated the separation of church and state laid down in the US constitution.

The “educational failure” of Cleveland schools left parents little choice but to send their children to private church schools, the court ruled, meaning the scheme was an illegal direct government subsidy. The state was offering about $2,500 (around pound;1,560) in vouchers to low-income parents.