The education secretary, Michael Gove, will be accused today of abandoning a promise to identify and turn around what he described in opposition as the "very worst" schools in England.

In a direct attack on Gove's claim that he is seeking to advance social mobility, Ed Balls, the shadow education secretary, will say at the Labour conference that the government has broken this pledge to struggling schools while encouraging those rated outstanding by Ofsted to convert to academies. He will also seek to stake out a distinctive view of education, by warning that the Tory focus on a "traditional" curriculum comes at the expense of subjects such as music or dance which help create well-rounded pupils.

He will say: "[Gove] says he wants schools now to focus only on 'academic' subjects, ... to shun what he sneeringly calls 'soft' subjects like design and technology, construction, music, sports or dance.

"I've been to countless schools over the last three years where headteachers have taken me to see a lesson in GCSE dance and said to me: 'Look at that class, it's not just that we have a great dance teacher in this school but the boost to aspiration and the belief and motivation of the students in this studio from this course will translate directly into their GCSE maths and English results as well."Balls, who won plaudits for an energetic campaign against the coalition's cuts to Labour's school buildings programme, will also publish research which appears to vindicate a key policy of the last government.

Under Labour's National Challenge scheme, introduced three years ago, ministers named 638 schools that fell below a benchmark of 30% of pupils getting at least five good GCSEs including English and maths. That number fell to 247 last year and the result of a survey of 100 of these struggling schools, carried out by Labour, shows that 78 met the pass rate target this summer and 13 others are on track to meet it by next year.

He will say: "I am proud that we transformed hundreds of schools across the country. And today we have not one in two schools below our National Challenge standard as in 1997, but just one in 20. But Michael Gove has shown he will abandon those schools to struggle."

At last year's Tory party conference, Gove pledged to identify the "very worst schools – the sink schools which have desperately failed their children" within the first 100 days of a new government. He said they would be put under the charge of heads with a "proven track record of success".

Balls will also renew his attack on the coalition's decision to end Building Schools for the Future. "In Sandwell, and Liverpool, and Nottingham and Brent and Wakefield, and in 80 local authorities around the country, Michael Gove has now told hundreds of thousands of children 'sorry, but you are not worth it,'" Balls will say. Public anger over the decision was compounded when the government published an incorrect list which showed that some projects had been spared when in fact they were being halted. The government believes the programme was wasteful and says that schools in urgent need of renovation will still get funding.

Balls will also describe the coalition's policy of encouraging "free schools" set up by groups of parents or teachers "as the most socially divisive education experiment for 60 years". He will draw attention to a faultline in the coalition by reminding his audience that the Liberal Democrat conference in Liverpool last week voted to campaign against free schools.

Earlier this month Gove announced the first 16 free schools to have won initial approval. The schools are due to open next September and include one in west London which will have compulsory Latin lessons, and another in Bedford where every child will be encouraged to play a musical instrument. The Lib Dems overwhelmingly backed a motion that attacked free schools because they risk "increasing social divisiveness and inequity in a system that is already unfair". Gove believes that a new generation of "independent state schools" with small classes and firm discipline will reduce inequality. He told his party's conference last year: "We will give parents control over the money which is spent on their children's education. Parents will be able to take the £5,000 the state spends on their children to the school of their choice. And we will give the parents of poorer children more money."