A spokeswoman for Cooper University Hospital in Camden says Natalie Tezsla's condition has been upgraded to stable, from critical. But her sister Sophie Tezsla remains in critical condition, as does a third student, 11-year-old Jonathan Zdybel.
The girls are the daughters of a New Jersey state trooper.
The crash Thursday in the town of Chesterfield, south of Trenton, killed the Tezslas' other sister - Isabelle.
The accident occurred when a dump truck collided with the school bus, which was carrying 25 children to Chesterfield Elementary in Burlington County. An investigation into the cause continues and no charges have been filed.
Meanwhile, grief counselors are on hand Friday at the elementary school.
People in the community gathered Thursday night to show their support for the grieving families.
Seventeen other students on the bus were treated for minor injuries.
Gov. Chris Christie called the crash "a terrible tragedy."
"The family's grief must be enormous," Christie said in a statement. "We can only imagine their pain and lend our support and prayers in this most difficult of times. We are sure that all of Chesterfield Township, the family of State Police men and women, and indeed residents all across New Jersey, have the Tezslas in their thoughts and prayers. Our same concerns and prayers extend to the other children aboard the bus, particularly Jonathan Zdybel, the young boy who also remains hospitalized and in critical condition."
The driver of the school bus was identified as John Tieman, 66, of Beverly, and the driver of the dump truck as Michael Caporale, 38, of New Egypt.
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