Children are arriving at nursery school able to "swipe a screen" but lacking the manipulative skills to play with building blocks, teachers have warned.

They fear that children are being given tablets to use "as a replacement for contact time with the parent" and say such habits are hindering progress at school.

Addressing the Association of Teachers and Lecturers conference in Manchester on Tuesday, Colin Kinney, a teacher from Northern Ireland, said excessive use of technology damages concentration and causes behavioural problems such as irritability and a lack of control.

"Teachers talk of students who come into their classrooms having spent most of the previous night playing computer games and their attention spans are so limited they might as well not be there," Kinney said.

"I've spoken to a number of nursery teachers who have concerns over the increasing numbers of young pupils who can swipe a screen but have little or no manipulative skills to play with building blocks – or pupils who can't socialise with other pupils, but whose parents talk proudly of their ability to use a tablet or smartphone."

Mark Montgomery, who teaches in Northern Ireland, added that when information is always instantly available to students, "there is less need to learn and retain knowledge". He told of how pupils at his school were struggling to learn lines for a play, something which had not proved difficult in previous years.

Teachers gathering in Manchester called for research into the effects of tablet addiction, and for advice on dealing with the issue among students.

Earlier in the day, the ATL passed an emergency motion expressing concern that the government has spent £637m on its flagship free schools programme, as well as millions more to help convert schools into academies.

Mark Baker, senior vice-president of ATL – the most moderate of the three teacher unions – told the conference there was a "culture of cronyism" underlying the academy and free schools programme, which he warned was "allowing corporate greed to destroy England's education system".

Referring to last month's TUC report, Education Not for Sale, he said: "We hear of the conflicts of interest, with at least three of the biggest academy chains being linked to the Conservative party through donation; the Harris Federation, the ARK Schools and the David Ross Foundation."

He added: "Private companies are thriving on the spoils of consultancy fees, legal and accountancy bills. Some £77m of taxpayers' money which could otherwise have been available for children's education."

The shadow education secretary, Tristram Hunt, told the conference a future Labour government would scrap the free schools policy, but keep existing free schools open.

Hunt said: "We've always said that we would keep open existing free schools and those in the pipeline, but because we have a highly politicised Department for Education there's a fear they're ramming the pipeline."

An ARK spokesman said: "As a charitable organisation, with no political affiliation, we're lucky to have support from a range of individuals and institutions. Some are politically affiliated, some not, and we have supporters from all the major parties.

"The money they raise for ARK is put into our schools and educational projects working in economically disadvantaged communities. The only interest we have is in delivering for the children we work with overseas and in our schools in England – all of which are rated good or outstanding by Ofsted."