Ed Balls has strongly criticised Conservative education reform plans.
The schools secretary accused the Tories of trying to re-establish a two-tier education system.
"Instead of breaking down the damaging old divide between 'excellent' academic qualifications for some and 'second class' for everybody else, the Tories seem determined to turn back the clock," he wrote in the Guardian.
"Our Diplomas, combining theoretical and applied learning, are our best chance to break this historic divide. They are widely backed by employers and universities and I'm determined to do everything we can to make them a success."
He also accused shadow schools secretary Michael Gove of taking a "deeply unfair, laissez faire" approach to education.
"Over the past year, Gove has set himself against this vision of excellence for all," Balls wrote.
"He dismisses our children's plan as a distraction. He opposes our radical reform to raise the education and training age to 18.
"And he refuses to match our guarantee this September of a place in school, college, training or an apprenticeship for every 16 and 17-year-old who wants to stay on."
Gove last week set out plans to remove some vocational qualifications from league table scores in a bid to give more weight to 'serious' academic achievement.
But some schools suggested that this could force them to abandon vocational courses.
GCSE results, also published on Thursday, revealed that one in five GCSEs resulted in an A or A* grade.
The number of pupils sitting exams in languages fell for a fourth year, after the government ruled that languages were non-compulsory for GCSE students.
But the pass rate for chemistry, biology and maths rose substantially.
