The details of last week's Year 6 Sats reading paper have been published, after some teachers and parents said it was so tough it left children in tears.
One question asked 10 and 11-year-olds to find a similar word to "eat" in a passage that contained both "consume" and "feeding".
Even staff "had to really think" about the answers, the National Association of Head Teachers (NAHT) said.
The Department for Education (DfE) said the Sats were "rigorously trialled".
BBC News was given the paper on Wednesday, so was able to look over the questions before their publication.
Concerns have been raised about its length and complexity, with some parents and teachers reporting that children were unable to finish it.
The paper has fuelled a debate among teachers and parents about the purpose of Sats.
In the test, children had one hour to answer 38 questions about three set texts.
The first was an extract from a story about friends who believe they have come across sheep "rustlers" - a word used in the text, which means someone who steals animals from farms.
Another was an interview about bats in Texas, which was based on a 2016 New York Times article.
The final passage was taken from a book called "The Rise of Wolves".
One head teacher identified what she thought were three of the toughest questions in a phone call with BBC News on Wednesday, before she had seen the mark scheme.
Look at Harriet's answer beginning It's actually very appropriate...
Find and copy one word that is closest in meaning to "eat".
Relevant extract: It's actually very appropriate that you call it a "hotspot". The gaps underneath the bridge are a perfect place for mother bats to raise their young. Baby bats are born hairless and have only a few months to develop before travelling south in autumn. They need somewhere warm and safe and the gaps under the bridge are just the right width to trap warmth nicely. These bat pups need to spend their energy on growth, not on keeping themselves warm.
Texas in general is a paradise for bats because of all its tasty insects. A mother bat will go out hunting every evening and consume about two-thirds of her body weight in insects every single night to meet her energy need. The feeding frenzy can last all night.
Answer: The teacher was concerned that the answer was "consume" but many children would have written "feeding". According to the mark scheme, both answers were acceptable.
She wriggled back inside the tent...
What does this tell you about how Priya got inside the tent? Tick one.
- She ran quickly inside.
- She jumped through the flap.
- She had to squeeze in.
- She crept in quietly.
Answer: The answer was that she had to squeeze in, but the teacher believed many children would have chosen crept in.
Look at the first two paragraphs.
In which American state is the Congress Avenue Bridge found?
Relevant extract: By day the Congress Avenue Bridge in the city of Austin could hardly look more normal: a grey, dreary city-centre road bridge. By night, it plays host to one of the most amazing shows nature has to offer. The underside of the bridge is home to more than a million bats, and every evening in summer they all come swarming out at once, rising up into the city sky like a tornado before spreading out in all directions like plumes of smoke. Standing on the bridge, you might even feel the wind from their wings as they pass by.
Austin is the capital city of the state of Texas in the USA, but it is also the bat capital of North America. The bats under the bridge attract thousands of visitors every year, and every August lovers celebrate Bat Fest on the bridge in their honour.
Answer: The answer is Texas but the teacher told us it was likely children would not be familiar enough with American geography to know that Austin is not a state.
Joe Saunders, from West Sussex, said his son Alfie does not usually talk too much about school at the end of the day, but "immediately" wanted to tell his parents about the Sats paper last Wednesday.
"Alfie, certainly in his case, was going into this having done really well in all his practices. He was completing all of his reading tests. So he had no concerns that he wasn't going to complete it," he said.
"Of the 15 or 20 that he's done over the last couple of months, the only one he hasn't completed or been able to complete is the one that he did last week, which makes it feel like something went wrong with that paper."
Simon Kidwell, NAHT vice-president and principal at Hartford Manor Primary School and Nursery in Cheshire, said children had "gone home really struggling because they hadn't finished the reading test".
"Staff had to really think about how they would answer those questions. So clearly it was quite a challenging, complex paper," he said.
Asked how hard he thought Sats papers should be, he said: "Children should be able to finish them."
The NAHT has raised concerns with the Standards and Testing Agency (STA), which delivers assessments, and Ofqual, England's exams regulator.
Gillian Hillier, chief executive of the STA, said this year's papers were "trialled with thousands of pupils" last April and had been developed over "at least three years".
"We use a range of rigorous and robust processes to ensure the tests are appropriate and fair, including reviews by teachers, curriculum and inclusion experts and other education professionals," she said.
There were measures in place to "ensure that each test is of similar difficulty to those in previous years", she added.
"As is the case every year, we will use data from the marked tests and trials to ensure the score needed to meet the expected standard reflects the relative difficulty of the test," Ms Hillier said.
"We will continue to engage with schools, unions and other stakeholders to understand their views on the papers this year, and in regard to all aspects of primary assessment."
A DfE spokesman said Sats were "an important way of identifying pupils' strengths and where they may have fallen behind as they head to secondary school".
Standard Assessment Tests, or Sats, are tests that children take in Year 6, at the end of Key Stage 2. They are national curriculum assessments in English grammar, punctuation and spelling, English reading and maths.
The government's Standards and Testing Agency says the purposes of Sats tests are to:
- help measure pupils' progress
- identify if they need any extra help in certain areas
- assess schools' performances
- produce national performance data.
Children also sit Sats in Year 2, at the end of Key Stage 1.
Additional reporting by Alice Evans.
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