Christina Regusters, 20, was charged with sexual assault, kidnapping, and other offenses. She is accused of dressing in Muslim garb and walking into the classroom to abduct the girl while posing as her mother.
Fernando Gallard, a School District spokesman, confirmed that Kline had sent the district a letter of intent to sue, but declined to comment further. "We don't comment on pending legal actions," he said.
Since the abduction, Bryant has adopted a tougher identification process for visitors. Two security officers now question visitors, and identification is required for entry to the school.
Students in Philadelphia's public schools may be released early only to an authorized parent or guardian, and only from the schools' office, not from a classroom, Gallard said. He said that the policy was in place before the girl's abduction.
Kline said the district had breached its duty to keep the child safe.
"I've viewed and still view the most pressing component of this terrible tragedy as bringing to justice all of the individuals who were involved in this heinous crime," he said.
Regusters' lawyer, W. Fred Harrison Jr., has suggested that someone else was responsible for the crime.
Regusters has been in custody since Feb. 14 on $4 million bail.
Contact Sulaiman Abdur-Rahman at firstname.lastname@example.org, or follow on Twitter @sabdurr.