The assessment and funding of pupils' special educational needs - both the responsibility of local authorities - should be split to avoid a conflict of interests, according to the Commons education select committee.
The MPs made the call last year, but were turned down by ministers who said it was the wrong time to take a "completely fresh look" at SEN. They said splitting the responsibilities would require the creation of a new assessment agency.
In its latest report the committee said: "If there are intractable problems, and our original inquiry certainly suggested that there are, it really is not good enough for the Government to say that nothing more can be done."
It argues the split could be achieved by either delegating SEN assessment to schools, by making education psychology services more independent, or by requiring local authorities or children's trusts to commission assessment from outside providers.
The MPs described the last option as the most practical: "It would allow the local authority or trust to set a specification, tender for services on the basis of that specification and then performance manage the subsequent contract."
It would mean the local authority still acting as the funder. Jim Knight, schools minister, made a commitment to consider practical suggestions for splitting SEN assessment from funding during a Parliamentary debate in January.
The committee also repeated its call for a national SEN strategy to set minimum standards and provide guidance on when statements should be issued.
They also want local authorities to publish documents setting out the SEN services and support they provide.