“We now have a situation where, aged four, some children have less than a third of the English vocabulary of their peers,” she will tell members of the Pre-School Learning Alliance.

“These children arrive at school without the words they need to communicate properly. Just imagine the disadvantage they face, right from the start.

“Unable to follow what’s going on. Unable to keep up with their classmates. Unable to reach their potential.”

Reading and literacy skills will also be a focus of Ms Spielman’s speech as “at the most basic level, poor literacy holds a person back at every stage.

“As a child, you will do worse at school. As a young adult, you may struggle to find work. And as a parent, you won’t be able to help your own children learn. This is a vicious cycle.”

Readiness for school

The Ofsted Chief will also reference the recent study that found 70% of schools reported more children starting school without being toilet trained compared to five years ago.

Ms Spielman has described it as a ‘simple but necessary expectation’ but does not suggest that nurseries become ‘substitute parents’.

“We know that the best nurseries work closely with families, helping to establish simple routines, such as sleep time and potty training, as well as introducing children to foods that they may refuse at home.”

She will also say today that children starting their first year of school should also be able to sit still and listen, understand the words “no” and “stop”, and be able to put on their own shoes and coat.

Obesity crisis

It was also reported this week that Ms Spielman has dismissed expectations that schools should address complex societal concerns such as childhood obesity.

She said:  “There are a great many pressing public policy concerns affecting young people. Many undoubtedly require government intervention and multifaceted solutions. But they cannot all fall to schools, and they often are completely inappropriate for measuring at inspection.

“I use obesity to illustrate the point, but there are countless other examples of where schools are expected to address every one of society’s ills and inspection is supposed to be the tool to ensure they do it.”