The teenager, who could not be named for legal reasons, is charged with planning terror attacks on the school and other local targets in Leicestershire in central England.
Speaking at the boy's trial, prosecutor Max Hill said the teenager kept a book called "Spree Killers" and had noted down the number of people killed at Columbine and by Anders Behring Brevik in Norway in 2011.
The defendant, who has Asperger's Syndrome, was arrested in February after being found with a machete. Police searching his home later found weapons, including ammunition, partially-assembled gasoline bombs and other explosives. He denies terrorism offenses but has admitted possessing bomb parts.
"He denied he had anything other than a genuine interest in the Columbine massacre," Hill said.
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Testifying at a London court, a science teacher at the boy's school said the defendant looked at guns online while he was at school and asked for advice about firearms and making explosives.
The teacher and another witness, a former friend of the accused, added that the boy was known to launch tirades abusing people of Muslim and Jewish faiths.