Having children pass a level 6 primary paper puts unrealistic pressure and expectations on secondary school children later on.
Our primary school headteacher is convinced that level 6 at keystage 2 is the equivalent of GCSE grade B. I believe that if a talented eleven year old with a level 6 in maths sat a GCSE higher level paper they would fail. Maybe a year 6 child with level 6 could pass foundation GCSE maths, but they have not covered the majority of the secondary school curriculum. I don't think that a primary level 6 is even the equivalent of a secondary level 6.
Many level 6 children have been moved down to the second set at ds's secondary because they have huge holes in their subject knowledge. I feel that primary school school should extend their gifted mathematicans sideways rather than pushing them through exams. (Ie. maths investigations, questions that require thought rather than mathematical knowledge ie. nrich.maths.org/frontpage) Improving mathematical thinking gives a good foundation for maths in later years.