"The family is sorry for the pain and trauma this event has caused. We are thankful for the understanding that people have shown. We love and support (him)," attorney James Gavin, reading a statement on behalf of the boy's family, said outside court.
The boy faces charges including aggravated assault, reckless endangerment, and risking and causing a catastrophe.
Witnesses said the boy, wearing a dark trench coat and listening to his MP3 player, barged into a first-period English class Wednesday morning and began slashing at students with a knife, flipping desks, throwing books and lighting firecrackers.
Three students suffered minor stab wounds before the eighth-grader was subdued by school officials.
Police said the boy brought to school a small can of gasoline, a water bottle filled with lantern fuel, firecrackers, knives and face masks to keep out fumes.
The boy has not spoken to prosecutors.
"We still don't know why he did this," Assistant District Attorney Catherine Nadirov said.
Gavin said the boy was "reserved, a little bit anxious" during Friday's hearing, which was closed to the public.
"This is a sad case involving an equally sad young boy," he said. "The family extends its sympathy and best wishes to those people who were hurt, and are seeking to have the greatest amount of help provided to their son."
A court hearing will be held after the police finish their investigation and the boy undergoes a psychological evaluation. If a judge finds him delinquent, he could be held in a youth facility until he is 21.
The school reopened under tight security on Thursday, with police searching every student with a handheld metal detector. Students could use only one entrance to get inside the building.
Superintendent Lawrence Mayes said school officials are reviewing security at the school in Lower Alsace Township, about 60 miles northwest of Philadelphia.
The school enrolls 540 students in grades seven through 12.
