Last week, she heard the proof herself as she sat in on one of the final debates of the National Association of Schoolmasters Union of Women Teachers' annual conference.
Delegates unanimously condemned the extension of selective admission policies, claiming such a move would undoubtedly lead to some schools being perceived as second-class.
They said the system was a result of political dogma and an obsession with league tables and called on the leadership of the union to mount a campaign to reassert the values of comprehensive education.
A move to publicise the "destructive effects" of selection by ability was defeated on the grounds that it could penalise union members working in grammar and independent schools.
John Harben, a member of the union's national executive, warned that increased selection could lead to the creation of sink schools "in which the problems of society concentrate and explode like a huge carbuncle.
"I don't want to see schools like that created anywhere in England. I want to see schools where every child and every teacher is happy and satisfied to work."
The union spoke out just days after the Government unveiled its general election manifesto, which included plans to establish grammar schools in every town where parents wanted that choice.
Mrs Shephard told journalists: "We don't wish to impose selection in any area." But she expected that the proposal would have enthusiastic support.
Concern over education policy was not limited to that propounded by Government. The conference also voiced its alarm over the growing tendency for schools to introduce weekend study and twilight learning sessions.
Labour has recently announced plans for homework clubs at premier football clubs such as Chelsea and Leeds.
Delegates to the Bournemouth conference heard that schools relied on teachers to run evening and weekend sessions in an attempt to boost GCSE A-C pass rates.