Liberal Democrats stepped up efforts to distance themselves from their Tory coalition government partners by accusing George Osborne of putting spending cuts before getting children out of poverty.
The party said a commitment to trial more effective anti-poverty targets "blocked" by the Chancellor would be included in its 2015 general election manifesto.
Gauging reductions in gaps in life chances and entrenched poverty could prove more effective than the present system which has "serious limitations", Education Minister David Laws said.
Splits over reforms to child poverty targets have dogged coalition efforts in the area - with Work and Pensions Secretary Iain Duncan Smith backing changes but the Treasury believed to be opposed.
Under the present measure based on average household incomes, a recession can lead to children who are no better off than before officially out of poverty.
Critics also complain that they fail to differentiate between families in long-term trouble and those with temporary difficulties and give governments no incentive to tackle the root causes.
Mr Duncan Smith signalled in February that proposals to rewrite the official definition of poverty had been shelved as he unveiled a new three-year strategy.
The inability to agree has been branded a "lamentable" farce by the Government's adviser on social mobility after estimates revealed the UK will be home to 3.5 million poor children by 2020.
Alongside the relative poverty measure, the Lib Dems want to record the number of families in poverty for 12 months or more, the number perceived as liable to fall into poverty because of long-term unemployment or low qualifications and the comparative GCSE results of pupils on free school meals.
Mr Laws, who is c hairing the Lib Dems' manifesto group, said: "The Conservatives have been keen to point up the failings of Labour's child poverty measures but less keen to replace them with decent, effective and supportive measures.
"Their desire to shrink the state by continuing to cut spending long after the deficit has been cleared trumped their rhetorical commitment to expanding opportunity for young people.
"Clearly a political dividing line on fiscal policy matters more to them than the effort to reduce poverty and expand life chances."
He went on: "Liberal Democrats know you can build a stronger economy and fairer society at the same time, and will not let political dogma, or headline chasing, damage someone's opportunity to get on in life.
"Labour's 'poverty plus a pound' strategy made a statistical impact but it left people's circumstances and future prospects largely unchanged.
"Our changes will change the focus in order to lift young people out of poverty for good by generating real opportunity.
"Rather than spending billions of borrowed pounds on welfare payments designed to move someone from just below to just above the official poverty line, we intend to invest in education and skills so people can work their way out of poverty and towards a future of self-reliance and success."
The party said the measures could initially be used alongside the existing Child Poverty Act "to give stakeholders, academics and others time to test their utility and robustness" before it was decided whether to enshrine them into law.