A judge who sentenced Aaron Knowles and Sam Thompson to a total of more than a decade in prison described the incident as 'shocking violence on the streets of Leeds'.
Leeds Crown Court heard how the boys were attacked as they queued to get haircuts outside a barbers shop in Beeston on May 12 last year.
John Batchelor, prosecuting, said it is thought the attackers were looking for revenge after one of their girlfriends was insulted earlier in the day.
The two 15-year-old victims were waiting outside the barbers on Dewsbury Road when they were approached by Knowles and Thompson.
The defendants accused the boys of "mouthing off" at them.
Mr Batchelor said: "It was suggested that they had a run-in with them earlier in the day but the complainants knew nothing about that".
Knowles then said to the victims: "I am going to stab someone".
Knowles punched one of the boys several times before chasing after him and stabbing him in the back with a pair of scissors.
The boy punched Knowles back and ran off.
He initially thought he had been punched in the back but then realised he had been stabbed.
He needed three stitches to a puncture wound.
Thompson pulled out a "menacing" blade which looked like a machete and chased the other boy.
Knowles also joined in the chase and stabbed the boy to the elbow when he fell over.
He was left bleeding from the wound and also needed medical treatment.
Police arrested both men after the incident and Knowles was found in possession of cannabis.
Knowles, 27, of Harlech Road, Beeston, pleaded guilty to two counts of attempted wounding with intent, possession of a blade in public and possession of cannabis.
He has previous convictions for violent offences including robbery, assault and prison mutiny.
Thompson, 25, of no fixed address, pleaded guilty to affray and possession of a blade in public.
He has previous convictions for robbery, affray, assault and theft.
One of the victims provided a statement to the court describing the impact the attack had had upon him.
He described how he was too scared to go to school after the incident and had suffered flashbacks to the ordeal.
Mr Batchelor said: "It keeps going around and around in his head. He keeps having to watch his back".
Michael Walsh, mitigating for Knowles, said the defendant was struggling with drug addiction at the time of the offences.
Mr Walsh said his client pleaded guilty to the offences at an early stage.
Michael Greenhalgh, mitigating for Thompson, said it was accepted that a prison sentence would have to be imposed for the offences.
Judge Simon Batiste gave Knowles an extended prison sentence of nine years and three months after a probation service report described him as "an extremely violent person who poses a high risk of serious harm".
He must serve a custodial term of five years and three months, two-thirds of which must be spent in prison before he can apply to the parole board for release.
Knowles must then serve a further four-year period on licence.
Thompson was jailed for two years.
Judge Batiste said: "It is shocking that violence of this sort is taking place on the streets of Leeds in broad daylight.
"It is clear the courts must do what they can to ensure this type of behaviour does not take place.
"You two both armed yourself with weapons in order to seek out persons for a perceived trifling slight which you were going to get revenge for."