An inquiry into the Department for Children, Schools and Families (DCSF) has revealed concerns over how well it works with the rest of Whitehall, particularly the Department for Innovation, Universities and Skills, with which it shares responsibility for 14-19 education.
"As yet, neither department appears to have taken the lead role," the Commons education select committee report said. "Given the importance of 14-19 diplomas, clarity over who is responsible is vital."
The report follows claims that overlapping responsibilities are leading to cabinet turf wars, with Jack Straw, justice secretary, reportedly threatening to punch Mr Balls, education secretary, in a row about responsibility for youth crime.
The committee said the DCSF was "possibly unique" in having responsibilities that overlap with eight others, and sole control over only early years and 5-13 schooling.
It welcomed the focus on children, but said: "The problem with joint responsibility is that it might mean no effective responsibility, with each part of the system doing its own work but with no one ensuring that it does all add up to coherent policy and actions."
A department spokesman said: "We've been crystal clear from the start that DCSF is in charge of all 14-19 curriculum and qualifications."
The report also warns that the Children's Plan risks being "a wish list" because it fails to give a timetable or spell out its priorities. It is also criticised for being based on new objectives, not Every Child Matters goals. And the committee points out that a promised bonfire of targets has not materialised.