More than 1,500 children starting secondary school this year in Wakefield finished primary education without meeting the Government standard, according to the Department for Education.
Key Stage 2 results for the 11-year-olds who took their SATs in May show that 40 per cent did not achieve the required score in all their tests - 1,546 children in all.
That's an attainment rate of 60 per cent - lower than the England average of 64 per cent.
This year, 3,866 Year 6 pupils took the tests, which are intended to measure how well a child is doing in three key subjects - reading, mathematics, and grammar.
They are also used to evaluate how well primary schools are preparing their pupils for secondary school.
Girls did slightly better than boys, with 64% of girls meeting the standard compared to 56% of boys.
But campaign group More than a Score says that schools looking to climb league tables focus too much on high SAT scores, and that SATs have "failed a generation of children".
It says that younger children, who can get anxious taking a test, should be assessed in a less stressful way.
During Year 6, students are also evaluated separately by their teachers in reading, writing, science and maths. These assessments provide a broader picture of how well children are doing at school.
Children in Wakefield did much better in KS2 teacher assessments than in the tests.
They did best in science, where 79% of pupils met the required standard, and worst in maths, where 76% of pupils made the grade.
More than a Score spokesperson Madeleine Holt said: "The apparent discrepancy between the KS2 SAT scores and the published teacher assessments shows just how unreliable the high-stakes accountability system has become."
She added: "A snapshot assessment of four years of academic work is likely to be intrinsically limited in what it tells you about a child."
The Association of School and College Leaders raised concerns that collecting two sets of results - SAT scores and teacher assessments - is "cumbersome and inconsistent".
Policy director Julie McCulloch said: "These two forms of assessment focus on different things, and reporting on both can be confusing and unhelpful."
Ms McCulloch said the ASCL was pleased that as of next year, reading and maths will be assessed based on SAT scores alone.
The Department for Education said that this year's results show how well schools have adapted to the higher expectations and greater challenge of the new primary curriculum, which is designed to "make sure they are prepared to succeed at secondary school".
It said that more pupils are now reaching the expected standard than in 2017.
School Standards Minister Nick Gibb said: "The Key Stage 2 tests play a vital role in ensuring that children have been taught, and have acquired a sound knowledge of, the fundamentals of reading, writing and mathematics.
"We trust schools not to put undue pressure on pupils when administering these assessments, and certainly not at the expense of their wellbeing.
"Thanks to our reforms and the hard work of teachers, education standards are rising in our schools, with 1.9 million more pupils in good or outstanding schools than in 2010."