In a separate vote, nine members of the school's advisory council chose Mastery and eight wanted a district-led transformation.
Citing the advisory council vote, Mastery officials claimed a victory.
Chief executive Scott Gordon, in a statement, said he was "thankful and humbled that the school's leaders, who visited Mastery schools and had the opportunity to carefully consider all options, decided that Mastery is the best choice for the Steel community."
Both votes are considered recommendations for Superintendent William R. Hite Jr., who in turn will make a recommendation to the School Reform Commission. The SRC has the final say.
Kendra Brooks, a Steel parent and member of the advisory council, said she was thrilled with the results, but not convinced parents' wishes would be honored.
"The SRC still gets to vote," Brooks said. "With the way this process has been botched, and rules have been changed, my level of trust in the district is slim to none."
Brooks and four other parents filed a grievance with the district's charter office, alleging that officials arbitrarily barred some advisory council parents from voting in the election. The process has been deeply flawed, she and others say.
"The charter office is making up the rules as it goes and breaking them whenever it feels like it," Brooks said.
Brooks and others have said the deck was stacked against Steel's remaining a district school, questioning why officials would be willing to spend an additional $4,000 per student if the district becomes a charter but will not allocate additional money to keep the school inside the district.
Jerry Jordan, president of the Philadelphia Federation of Teachers, which was heavily involved in organizing parents to reject the charter option, urged Hite and the SRC to honor parents' wishes.
"The parents at Steel have chosen a collaborative transformation plan for the school, and are sending a clear message to the SRC, the School District, and the city: We believe in the promise of neighborhood public schools in Philadelphia," Jordan said in a statement.
This year's "Renaissance" process of turning around struggling schools has been particularly chaotic. It started late and was bitterly fought.
The district opted to postpone the vote at Munoz-Marin, the other school slated for possible conversion, but went forward at Steel.