The alleged victim died from a stab wound to his thigh after a confrontation at a park behind a school in northwest Sydney on Monday afternoon.
A 15-year-old boy accused of inflicting the fatal wound is in custody charged with murder.
Police arrested a second boy, also 15, over the alleged attack after arriving at his home near the crime scene about 9.45pm on Tuesday.
Charged with murder overnight, the slender teenager appeared solemn and afraid when he faced a children's court on Wednesday morning.
His parents, seated in court, were distraught with the mother on the verge of tears.
Magistrate Megan Heywood explained the court process to the boy as he sat silently in a brief hearing.
The teenager, who cannot be identified for legal reasons, did not apply for bail and will remain in custody until his next court hearing, slated for late January.
Police are expected to detail the specific allegations against him in a later press conference.
According to a police statement read in court on Tuesday, the other 15-year-old allegedly set upon the victim unprovoked and stabbed him in the groin area.
The wounded boy could not be saved despite assistance from witnesses.
"I stabbed another boy in the leg," the boy later told police in a conversation caught on body-worn camera footage.
The death has rocked the community, which occurred in a Rouse Hill park and within sight of multiple people who were walking nearby.
Several laid flowers in honour of the 17-year-old hours after his death.
Friends of the slain teenager continue to leave moving tributes to him on social media, remembering him fondly.
"We all miss you so much and you are so loved .... you did not deserve any of this. You had the kindest soul," one of his friends said in a video.
His girlfriend meanwhile remembered the boy as beautiful, strong and who "deserve(d) the world."
"I wish I could have saved you," she posted online.
Police said those involved in Monday's confrontation were not from a nearby high school and officers believe it was not a random attack.
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