The teenager, who cannot be named for legal reasons, has been found guilty of the three charges following a trial at Swansea Crown Court.
She had previously admitted to three counts of causing grievous bodily harm with intent, and possession of a bladed article on a school premises.
She now awaits sentencing.
Emergency services were called to Ysgol Dyffryn Aman in Carmarthenshire on Wednesday, April 24, following reports that three people had been injured.
Two teachers – Fiona Elias and Liz Hopkin – along with a child, were admitted to hospital for treatment having been stabbed.
CCTV cameras captured the girl walking through the school on the Wednesday morning, before stabbing the floor in the hall with a knife.
She was then seen speaking to Mrs Elias on two occasions – inside and outside the school building – before attacking her with a knife. When Mrs Hopkin stepped in to help, she was also injured.
A few minutes later, after being taken away from the two teachers, she was seen attacking a child with the same knife.
Detective Chief Superintendent Ross Evans said: “This was an incredibly distressing incident, which not only resulted in three people being physically harmed, but also had a profound impact on the wellbeing of pupils who were present at the time. We wish them well as they continue to recover from an incident they should never had to witness at such young ages.
“School should be a safe place, a sanctuary for the pupils that attend it, and weapons have no place within their grounds. We will not tolerate any attempt to compromise the safety of children or staff, and as demonstrated here we will act swiftly on the very rare occasion they are put at risk.
“I would like to thank all my emergency services colleagues who responded on the day, along with the teachers and staff at Ysgol Dyffryn Aman and Carmarthenshire County Council for the way in which they dealt with the incident, and the local community for the support they offered to pupils at the school.
“Now that criminal proceedings have come to an end, I ask that we let life at Dyffryn Aman get back to normal so the pupils and staff can focus on their education.”
Cllr Darren Price, Leader of Carmarthenshire County Council said: “Following today’s verdict, Carmarthenshire County Council wishes to reiterate its heartfelt sympathies to the victims of the incident and the entire community of Ysgol Dyffryn Aman.
“The incident that took place at the school on 24 April 2024 shocked and appalled the communities of Carmarthenshire and beyond. Violence, in any form, has unequivocally no place within our schools or any aspect of society.
“I would again like to thank the emergency services that responded at pace during this incident; along with the teachers, staff, pupils, council officers and the local community.
“I am also grateful to Dyfed Powys Police for their diligent work in the hours, days and weeks following the incident; we as a local authority greatly value our working partnership.
“On completion of the trial, all partners will be working together to review the circumstances of this case and to ensure we do all we can to prevent an incident of this nature happening again.
“The resilience and compassion that define the close-knit society of Ysgol Dyffryn Aman has allowed pupils to return to their classrooms at the safest and earliest opportunity, for their benefit and wellbeing.
“I sincerely hope that today’s verdict will permit the victims and the school a sense of closure on this awful event and that their privacy is respected. Ysgol Dyffryn Aman is an excellent school and long may it continue its excellent work in educating the children and young people of Ammanford.”