School bosses say pupils are paying the price because of a lack of decent government investment.
The Tory leader accuses PM of "vandalism" but Sir Keir says the Schools Bill will protect vulnerable children.
A conference arranged by the campaign group Smartphone Free Childhood, takes place on Thursday.
The union and school bosses are to meet on Friday for talks aimed at resolving the dispute.
The children's laureate says a "recession in children's happiness" is caused by a decline in reading.
Kray says Birmingham City Council failed to provide an education plan within the legal timeframe.
University of Brighton Academies Trust runs 11 primary schools and three secondary schools.
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