National tests for 11-year-olds in England this year have shown a slight improvement in the proportion reaching the government’s expected standards in maths and literacy by the time they finish primary school.

Results for the standard attainment tests, known as Sats, taken at the end of key stage 2 found 65% met the government’s targets, compared with 64% last year and 61% in 2017, although attainment in maths and reading scores moved in opposite directions.

In maths the national figures showed a stronger improvement, with the percentage reaching the expected standard rising from 76% in 2018 to 79% this year. But tests of reading fell from 75% to 73%, although teacher-assessed scores for writing were unchanged at 78%.

Nick Gibb, the school standards minister England, said the results showed the majority of pupils were leaving primary school ready for the challenges of secondary school.

“The pupils who performed well in these tests will have demonstrated sophisticated grammatical skills like using the subjunctive, the ability to divide fractions and mastery of complex spellings,” said Gibb.

“It’s testament to the hard work and dedication of teachers that we have seen results rising over time despite the bar of expectation having been raised.”

The interim results are the first to come from the tests taken in May by pupils in year 6, the final year of primary school. The results are mainly used to monitor school effectiveness by the Department for Education (DfE), with a more detailed breakdown of results to follow later in the year.

But teaching unions remain opposed to the tests because of the stress they cause for teachers and pupils.

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“Sats results and league tables provide nothing more than a snapshot of how children performed on a particular day, in a few short tests, in a limited number of subjects. We should therefore avoid celebrating too loudly or berating too strongly schools that rise or fall,” said Nick Brook, the deputy general secretary of the National Association of Head Teachers (NAHT).

The testing of children to measure school performance has become a controversial political issue, with Jeremy Corbyn telling teachers in April that a Labour government would abolish Sats in England. The Liberal Democrats had previously pledged to abolish the tests at key stage 2 along with school league tables.

Brook said the NAHT wanted fewer formal tests in primary schools: “Sats tell teachers and parents little that they don’t already know about their child or school, but have the negative unintended consequences of distracting from teaching and learning and narrowing the focus of the curriculum.”

In recent years some schools have run Easter holiday revision sessions, while parents have complained that schools devote too much time to Sats preparation.

Kevin Courtney, the joint general secretary of the National Education Union, said the results meant a third of pupils would be entering secondary education in September branded as below standard.

“This demoralising outcome is the result of policymakers’ delusion that to measure the performance of our primary school system it is necessary to test each individual pupil,” Courtney said.

The DfE said failing to reach the expected standard did not mean those pupils were unable to read or count. “There’s a spectrum of attainment among pupils who do not meet the expected standard, with some coming close and others further away,” the department said.

More Than a Score, a group that campaigns against Sats, said the results came at a heavy price for pupils. “Many of those pupils will have spent months focusing on just English and maths to prepare for Sats. They will have missed out on a broad and stimulating curriculum at a critical point in their education,” said Sara Tomlinson, a spokesperson for the group.