The new phonics tests for six-year-olds in England is successfully identifying children who struggle to read, but is no more informative than existing teacher assessment, research suggests.
The research, by Oxford and York universities, also queried a screening test which had "no prescribed course of action" for pupils who were struggling.
The phonics check requires pupils to read aloud 40 real and made-up words.
Ministers said it identified those who needed further help learning to read.
The phonics screening check will be used for the second time in England's schools later this month among pupils who are coming up to the end of Year 1.
The check was introduced in 2012 as a compulsory assessment, but has been controversial because it tests children's ability to decode words using a single method, phonics, rather than their ability to read itself.
In a study of 300 pupils at eight primary schools in York, representing a cross-section of socio-economic groups, researchers measured pupils' scores in the statutory phonics check against regular phonics progress checks (known as the six phonics phases) carried out routinely by teachers.
They also measured pupils' phonics check scores against other standardised reading and spelling tests.
They concluded that while the government test was accurate in identifying children who were struggling, it offered no information that teacher assessment did not already provide.
Report author Professor Maggie Snowling from the Department of Experimental Psychology at Oxford University and president of St John's College said: "The phonics screening check is a based on sound principles, but I don't think it's necessarily the best way to check on progress.
"The new phonics check raises issues about costs and benefits of testing versus teachers being well trained to monitor children's progress."
Prof Snowling, who carried out advisory work for the Department for Education on the design of the test, said she had concerns about a lack of measures in place for those pupils identified as having difficulties with reading.
"The new phonics screening check is successful in helping teachers identify children who need extra help in learning to read.
"But there is faulty logic here it seems to me. This 'reaches' or 'fails to reach' the standard in a one-off test gives no sense of why the child has difficulties or what should happen next.
"What do you do with kids who are identified as failing? While there is guidance for schools there is no specific funding which follows the identification of children failing to reach the standard in their phonics skills.
"Ethically I think it is questionable to offer screening with no prescribed course of action for those who are identified as at risk."
A spokeswoman for the Department for Education said: "Too many children are not reaching the expected levels of reading at a young age, do not catch up, and then struggle in secondary school and beyond.
"The phonics check is based on an internationally proven method and will ensure children struggling with reading get the help they desperately need.
"Teachers identified more than 235,000 six-year-olds behind on reading last year - demonstrating its value."