It says 65% of primary schools and 54% of secondary schools complained about a lack of wi-fi connectivity.
Nearly half of primary schools and a third of secondary schools reported inadequate broadband.
The authors from the British Educational Suppliers Association (Besa) called on the government to fix the issue.
The report found that there is a big correlation between those schools with poor use of ICT in the classroom and the UK's broadband not-spots as identified by Ofcom.
Areas where schools are struggling with bandwidth issues include Cumbria in England, East Ayrshire in Scotland and Gwynedd in Wales.
"It is of great concern that pupils are being denied access to innovative and effective digital learning because of poor internet connectivity in more than half of the UK's schools," said Besa's director Caroline Wright.
"In today's digital society, classroom connectivity to an online world of knowledge and resources should be a right for every student in their place of learning and not a lottery."
Schools that are struggling with poor internet access also report low uptake of tablet computers, risking a big digital divide opening, warned Ms Wright.
"If a teacher standing at the front of the class knows that they have unreliable wi-fi they are less likely to use internet-connected resources and devices," she said.
She called on the government to "take speedy action" to make sure all children could benefit from "an education that harnesses the power of educational technology".
Andrew Ferguson, founder of broadband news site ThinkBroadband, put into perspective the challenge many schools face when it comes to providing adequate bandwidth.
"A class of 30 pupils doing media-rich research can easily fill a 100 Mbps connection and without sufficient management of the connection it is possible for one pupil to use all the available bandwidth."
The findings are not all bad though.
The report found that schools are rapidly increasing the number of laptops in classrooms and many are using lower-cost tablets to offer more children access to a device during lessons.
Source: bbc.com
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