The teenager has also been charged with possession of ammunition with intent to endanger life and having a pocket knife on school premises, Warwickshire Police said.
The youth, who can not be named because of his age, dialled 999 after having "a change of heart" and told a call-handler he had mental health problems and had been thinking of harming others.
The boy has also been charged with possession of ammunition with intention to endanger life and possession of an article with a blade on school premises.
Armed officers were called to Higham Lane School in Shanklin Drive, Nuneaton, at 9.15am on Tuesday (13 June).
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Magistrates bailed the boy to an address outside Warwickshire before he is sentenced at Warwick Crown Court on July 14.
Mr Majid told the court: "When he went to the school he had concealed these items on him". He said "I don't know why I've got it, I just felt so angry this morning and I had to get it out".
In a statement on the school's website, head teacher Phil Kelly assured parents the school "will continue to be vigilant and will take all necessary precautions to ensure our children's safety".
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