The first official crackdown on malpractice in the employment of teaching assistants is set to begin next term.
Schools will be told for the first time to pay support staff a fair wage and stop using them to teach lessons they are unqualified to take.
The guidance, which is expected to be enforced by advisers from the Teacher Development Agency for Schools, is backed by the Government, unions and employers.
It comes in the wake of last term's Unison strike that saw thousands of assistants walk out of schools.
The growing significance of support staff has been shown by research by the British Educational Suppliers Association.
Asked what their main spending priorities were for the coming year, primary heads were more likely to say teaching assistants than teachers, while secondary heads saw them as of equal importance.
The new guidance tells schools: "Ensure that support staff receive fair and consistent pay and conditions appropriate to the overall role and responsibilities they undertake."
The strongly worded document amounts to the first official recognition of widespread malpractice among schools from the headteachers and the Department for Children, Schools and Families. Support staff unions had to battle hard for its publication.
It warns of "widespread confusion" from schools over what roles different support staff should be performing in the classroom.
The unions want a review of the situation in six months. If there has been no improvement they will be pushing for tighter legislation to force schools to improve their members' working conditions. The document identifies three major areas of concern in the way support staff are paid.
It cites research from the biggest support staff union, Unison, which last year found up to half of schools were using split contracts that only pay teaching assistants higher level rates for the hours when they are doing "higher level" work.
The guidance also tells schools to review their use of term-time only contracts which it says the majority of support staff still have.
It also deems the practice of expecting support staff to work beyond their contracts on unpaid overtime as "unacceptable".
The guidance points to "widespread confusion" between the two "very different" new roles created for support staff by the school workforce agreement - cover supervising and taking classes during a teacher's timetabled preparation time.
The TES reported earlier this year that there have been increasing fears of some schools using cover supervisors unqualified to teach as "cut-price teachers" which the guidance says is "inappropriate".
Christina McAnea, head of education at Unison, said she fears schools, particularly primaries, are either using untrained support staff to cover preparation time or using staff that have been trained without paying them the proper rate.
"We hope this guidance will give us some ammunition to stop the worst practices that take place in schools," she said.
Kerry George, senior assistant sec retary of the National Association of Head Teachers said: "I am not convinced there is any willful abuse of these staff."