Fifteen years after Margaret Thatcher's government introduced the clause, the law suffered a near-fatal blow last week.
Baroness Blatch, Conservative education spokeswoman in the House of Lords, failed in a bid to block a government move to scrap the clause. She had tabled an amendment to the Local Government Bill which would have strengthened Section 28 by providing for parents to be sent copies of any book, video or teaching aid used in sex education.
But this was defeated by 180 votes to 130. Baroness Thatcher voted in favour of Lady Blatch's amendment.
The Bill will not complete its passage through Parliament until the autumn, and there is still the possibility of a challenge when it returns to the Lords in September.
But opponents are hopeful that the margin of the defeat means future amendments supporting the clause will fail.
John Bangs, head of education at the National Union of Teachers, said: "The purpose of Section 28 was to intimidate teachers and young people.
Removing this nasty little piece of legislation has taken a long time, but we should all celebrate its demise."
The National Association of Schoolmasters Union of Women Teachers and the Association of Teachers and Lecturers also welcomed the amendment's defeat, as did the National Children's Bureau.