The rising number of teaching assistants in England's classrooms is part of a "creeping amateurism" in schools, one of education’s most influential professors has said.
Professor John Hattie, director of the Melbourne Education Research Institute and one of the world’s most widely quoted education academics, also said that the country's obsession with different types of school was doing "incredible damage", and that classroom observation was a waste of time.
Speaking at the Association of School and College Leaders' annual conference in Birmingham today, Professor Hattie said: "I see this creeping amateurism coming into our business. I know in your country now, over 20 per cent of your salary budget – 20 per cent – you pay to the amateurs."
He said that TAs "systematically" have the lowest impact on students' learning, and that the bulge in their number was "toxic".
Earlier this year Tes revealed that extra teaching assistants had swallowed up more of the extra funding going to schools over the past two decades than anything else.
Professor Hattie said: "We also know that those TAs are usually assigned to the kids that need most expertise.
"We also know that many of those TAs are lovely people, and parents like them, and teachers like them. But their effects size is down the bottom."
It is not the first time he has criticised TAs. In an interview with Tes in 2015, he said it was "ironic that the students who need the most expertise get the adults with the least expertise”.
During his conference speech, Professor Hattie said that parents and teachers prioritised things in education – such as smaller class sizes – which had a "trivial" impact on outcomes.
"Parents and teachers most often want things that do most harm to their kids. Sorry – that's the data."
In particular, he said that parents "want all the structural things that don’t make much difference".
"They want to have a debate at their dinner tables about the choice of school their kids go to."
He continued: "Wow, your country has been obsessed about the differences between different types of schools.
"If you’re going to allow that kind of narrative to happen – which means that politicians have that narrative, because they’re appealing to those parents – you are doing incredible damage to the nature of the schooling system.”
Professor Hattie also criticised the increasing popularity of classroom observation.
"I struggle to find any evidence that it makes any difference to anything other than the person who’s at the back, telling you how you can better teach like they do," he said.
“Many people say to me, "Come to my school and look at it.' Look at me – I’m not a student. I’m not 10, I’m not 15. I can’t see your classroom by sitting at the back of it in the same way the students can.”