Investigators initially reported that the altercation involved students at Simon Gratz High School, Fels High School, and Hartranft School.
A 17-year-old Fels student was shot in an arm and a 14-year-old Hartranft student was shot in a leg, police said.
When Lanier's parents surrendered him to authorities Thursday, police said it appeared Lanier did not attend school.
Lanier, however, was attending Upper Darby. He transferred last November from Gratz, said Upper Darby Police Superintendent Michael Chitwood.
He had to provide a letter describing his circumstances, Chitwood said. Lanier told the school he was living with his sister, now 22, in the 500 block of Snowden Road in Upper Darby, Chitwood said. Lanier said that his father lived in Philadelphia and that his mother was dead.
"It was a ruse" to get into Upper Darby High, Chitwood said. The school was about to expel him because of that, Chitwood said.
On Tuesday, the school called Upper Darby police to report that Lanier had been caught with marijuana. He was arrested and issued a citation, Chitwood said.
Unable to attend classes Wednesday because of his suspension, Lanier returned to Philadelphia.
The subway altercation and shooting were related to a previous fight, police said.
Both shooting victims were taken to Temple University Hospital. The older teen has been released from the hospital.
The 14-year-old was transferred to St. Christopher's Hospital for Children and was still in critical condition Friday.
Lanier also is charged with aggravated assault, reckless endangerment, burglary, trespassing, and gun possession.
Contact Jessica Parks at 215-854-4851 or firstname.lastname@example.org.