The question, included in last week's level 5-7 paper one, asked pupils to factorise the expression 6y3 - 2y2 as fully as possible.
But schools complained that this was level 8 material and should not have been included in the test.
Brian McBurnie, deputy head of Sir Thomas Rich's Grammar Schol, in Gloucester, said: "If we are going to set such great store by these tests then the QCA must abide by their own rules about what is to be included in them."
Factorisation is covered in the level 8 attainment description but not level 7. The target says that pupils working at level 8 should: "manipulate algebraic formulae, equations and expressions, finding common factors and multiplying two linear expressions."