Child poverty is on the increase, and it matters.

Even a temporary drop into poverty has long-lasting and profound effects on children’s lives. For those children raised in persistent poverty, the effects are lifelong.

Sadly, despite Theresa May’s commitment to help those families who are “just about managing”, the rise of child poverty continues apace.

In December 2015, the Social Mobility and Child Poverty Commission warned that after a decade and a half in which child poverty fell significantly, it was likely to rise in the years to 2020. The latest figures show that 4 million children in the UK were living in poverty in 2015-16, and this could rise to 5 million by 2020, according to the End Child Poverty campaign. So this is an issue that affects the many, not the few.

A recent report by the Royal College of Paediatrics and Child Health and the Child Poverty Action Group shows just how poverty impacts on a child’s life: poor children have less to eat, and more of what they do eat is unhealthy. They are more prone to respiratory illnesses caused or exacerbated by cold, damp housing. And they are more susceptible to mental health problems caused by family financial stresses.

There can be no doubt that poverty matters when it comes to educational achievement. Inequality begins at birth and grows. Developmental gaps of nine months between advantaged and disadvantaged three-year-olds double to 18 months for four-year-olds. It has been estimated that children from high-income families are exposed to about 30 million more words than children from low-income families.

The cultural and leisure experiences which advantaged children enjoy are little more than a mirage for their poorer peers, whose lives are much more likely to be marred by parental stress, family dysfunction, poor housing and bad diet. Teachers see the effects of poverty every day. They know which children will go home to a warm house, with decent food, and parents who are not so stressed that they can’t listen to their child read. Teachers strive, every day, to overcome the disadvantages and developmental delays that poverty brings.

But this is, ultimately, an unequal struggle because schools and teachers cannot, like King Canute, stand firm against the rising tide of inequality and poverty. Alarmingly, school leaders are seeing the support they need to help disadvantaged children being stripped away. The Local Government Association has said councils are not able to meet the rising demands for child support and safeguarding services because of cuts. Spending by English councils on children’s services has dropped by at least 9 per cent since 2010 - and, since then, the number of children in need has risen by 5 per cent.

Although councils are meeting the most urgent safeguarding needs, this has been at the expense of services like Sure Start, parenting courses and youth work. And who is left to deal with the problems when no support is available to families? Teachers, school leaders and education support staff, of course.

If Theresa May wishes her words about a fair and just society to be more than that - just words - she should ensure that her government acts to reverse the rising tide of child poverty. I look forward to reading her proposals, in the Conservative Party manifesto.

Mary Bousted is general secretary of the ATL teaching union. She tweets @MaryBoustedATL