Education watchdog Ofsted has grown "enormously" and faces the risk of becoming "unwieldy", a new report claims.
The Children, Schools and Families Committee report into school accountability also warns against Government plans to rate schools with a single grade on a US-style report card.
Committee chairman Barry Sheerman said: "We now have an accountability framework which is far too complex and which stigmatises and undermines struggling schools."
He added: "What schools need now is a period of stability and a chance for their own efforts to improve performance to bear fruit."
The report also questions whether Ofsted's work inspecting not just schools but colleges and children's services is "sustainable" in the long term.
It states: "Both Ofsted and the Government should be alert to any sign that the growth of Ofsted's responsibilities is causing it to become unwieldy or uncoordinated."
On the subject of report cards for schools, the study states: "A report card can never be a full account of a school's performance, yet the inclusion of an overall score would suggest that it was."
Research carried out last year by the Department for Children, Schools and Families suggested that parents opposed the plan, which was proposed by Schools Secretary Ed Balls in 2008.
Many were worried it would "stigmatise" poorly performing schools, and result in lower esteem among pupils and teachers.
Under the system, state schools will be ranked on a number of measures, including behaviour, attendance and take-up of sport, as well as academic performance - and given a final overall grade.
