The fifteen-year-old, who cannot be named for legal reasons, allegedly attacked teacher Ann Maguire in front of a classroom of pupils at Corpus Christi Catholic College on Monday.
61-year-old Ann, who had planned to retire this year, suffered more than six knife wounds in the attack, mainly to the neck and back.
According to another pupil at the school, Mrs Maguire's attacker had just come out of a relationship with a secret girlfriend.
'He confided in a couple of people that he was seeing this girl but then she ended it.'
'I think he was far more into her than she was into him.'
The pupil added: 'It was his first girlfriend because he was the kind of lad who kept himself apart from the rest of the class and didn't act or dress like the other lads.'
During the attack Mrs Maguire fled the classroom before collapsing in a pool of blood in front of another room full of teenagers. She was pronounced dead at hospital.
The defendant is appearing at Leeds youth court today and then will appear at the crown court on Friday.