The violent act involved a dispute over apricot jam, Granada's Ideal newspaper reported on Monday.
A young couple, both aged under 18, were making breakfast when the incident happened.
The young man was preparing toast when his girlfriend repeatedly insisted that she wanted apricot jam on her next slice.
She said this on various occasions until her boyfriend flipped out and "launched" the knife at the girl's head.
The kitchen utensil then struck her on the forehead. Fortunately the only result was light bruising.
When the young woman went to a local health centre, staff were unworried by the injury.
The boy later confessed to the knife attack and has now been sentenced for causing bodily harm. As a minor, however, he has received only a one-year probationary sentence.
If he breaks the terms of his sentence, he could end up in a correctional facility for juveniles.
The boy will also undergo counselling for anger management and to help him understand that violence against women is unacceptable.
According to judicial reports, the knife tossing incident was the final straw for the adolescent. Apparently the boy involved in the case was living with his girlfriend and his mother in a situation the court described as "turbulent".
The court also said the assault was the latest example of ongoing aggressive behaviour — both physical and psychological — on the part of the teen.
Reports also stated the boy's girlfriend was living in fear and that a judicial sentence was necessary to make him understand the consequences of his actions.
The boy's family knew he was keeping bad company, Ideal reported. He was also known to be taking drugs.