A troubled Perth teenager who tried to kill a "trusted" teacher told the victim she had "a good surprise" for her before lunging at her with a 32-centimetre knife with "a calm and intent look on her face", the Perth Children's Court has been told.
The girl, who cannot be identified, was 14 years old in November last year when she brought the knife to Willetton Senior High School from home with the intention of using it to fatally stab the 55-year-old victim.
