Nearly half the titles read by children in a new national schools reading competition were read online, says literacy charity Booktrust.
Read for My School 2013 aimed to boost the numbers of primary pupils in England reading for pleasure.
Almost 100,000 nine to 11-year-olds, from 3,600 schools signed up.
"Children were sitting in their rooms using their iPads and Xboxes to read rather than for games," said Alison Keeley of Booktrust.
Between them, the children who took part read more than 400,000 books. Some 49% of these were read online from a free digital library of 46 titles from Penguin, Dorling Kindersley and Pearson.
A poll of their teachers suggested the e-library was particularly popular among boys and less-proficient readers.
"I think boys and poorer readers just prefer reading online. It's about making it different and more exciting, a different way to use their Xbox or iPad.
"The competition website allowed us to tell what format they were reading on. Some children were particularly motivated by the competition element", said Ms Keeley.
Comments from teachers suggested that suddenly the keenest readers "had their standing in class transformed", she added.
The competition, organised by Booktrust and The Pearson Foundation with support from the Department for Education, ran from January to March 2013.
Children had to log the books they read on the competition website and answer questions to prove that they had not just flicked through the pages.
They could choose from the 46 titles in the e-library or read any title they fancied in traditional book form as long as it fitted into one of eight competition categories.
The idea was to broaden children's reading tastes as they had to read at least one book from each category, ranging from "Laugh out Loud" funny reads to "Keep it Real" factual books and including history, animal stories , sci-fi, mystery and thrillers.
Megan Benson, aged nine, from Devon won the prize for most prolific reader, devouring 273 books during the competition. Jack Casey, 10, from Wiltshire won the prize for the most interesting written responses to the books he read.
The most popular books in the e-library were a historical tale based on the sinking of the Titanic, a comedy version of Cinderella and a factual account of the story of chocolate. Overall comedy was the most popular category.
Children's author Jeremy Strong said: "I'm not at all surprised to see that funny books have come out top in this brilliant reading competition. I've always felt strongly that adding a sense of fun to stories is the best way to turn a child into a reader so I'm delighted to hear that thousands of children across the country feel the same."
Education minister Elizabeth Truss added: "I am delighted the competition has encouraged even the most reluctant children to pick up a book for the first time."