"I have to set the standard," he said. "I want to let them know that I had big dreams when I was in ninth grade and I went for them. I want them to know they can go to Princeton."
It's volunteers like Nnannabu that help school personnel across the city to meet the daunting task of fulfilling not only students' academic goals, but their social and emotional needs as well.
To help meet the diverse demands of the city's children, hundreds of individuals, and volunteer and service groups, have stepped in to help fill the void.
Over the last several years, the services that volunteer groups provide in many of the district's schools have evolved. Some now invest time and resources in addressing the dropout and truancy rates, while others offer business workshops.
Even more serve as mentors, tutors and confidants, while a few have gone so far as to give their disadvantaged charges food and clothes.
It's that kind of support in schools that makes a difference in the lives of students, said Ethelyn Young, principal at Overbrook, which has several outside groups serving the school's roughly 1,600 students in various capacities, including help with homework, sessions on conflict resolution and martial arts.
"I couldn't do it without them," she said of the several volunteer groups that work in her school. "They bring energy, new ideas and passion. They're here 'round the clock. You can't beat that."
Some of the groups, like national nonprofits City Year and Communities in Schools, get some money from the district to provide services - including home visits, counseling and socialized recess - while smaller, unpaid nonprofits like the Black Clergy of Philadelphia and Vicinity offer small-business workshops to a handful of kids in a few schools.
Also contributing numerous hours in schools are parents and grandparents, who perform duties from assisting teachers with paperwork and fielding calls in the front office to escorting younger students to the bathroom.
"We don't have the resources to get to all the children," Young said of Overbrook High. "That's why they fall behind. [The volunteers] let them know that they [students] are cared for."
At her school, it cost roughly $35,000 last year to pay the stipends of eight City Year corps members who are assigned 30 to 35 students during and after school, she said.
She said it's worth the investment. District officials appear to agree.
This school year alone, the district has approved more than $2 million in contracts for three of the country's largest volunteer organizations to operate programs in 57 schools.
Here are profiles of a few of those volunteering in district schools:
* Education Works corps member Charles Corley, 21, said he was lucky enough to have people in his life as a youngster to keep him out of trouble. But that wasn't the case for many of his peers, he said.
Now he goes out of his way to make the fourth-to-eighth-graders, especially the boys, whom he mentors - at Cleveland Elementary, on 19th Street near Erie Avenue, in Nicetown - "comfortable and happy."
"If it weren't for people helping me, who knows where I would be?" said the Strawberry Mansion resident. "I want to teach them how to be better people."
Many of the students come from homes where drugs and violence are the norm, he said. Frequent phone calls and home visits are necessary to encourage kids to stay focused on their studies. And as often as he can, he takes students out to dinner, and gives some of the needier ones clothes and food.
"I want to broaden their horizons," he said. "I don't want them to progress just for a moment. They need to progress for life."
* For West Philly native Felicia Cooper, 21, volunteering at Overbrook High as a City Year corps member was like a homecoming of sorts.
"I came to City Year because I am from the School District of Philadelphia, so I know some of the challenges as a student that could be faced," said the graduate of Edward W. Bok Technical High School and Lehigh University.
It's for that reason that she dedicates hours working with students pegged as at-risk. She connected with one student in particular, a freshman whose problems with behavior and attendance haven't helped improve her sluggish math and reading skills, she said.
For more than a month, almost every day in the library, the pair sounds out words that the student can't make out and work on her math homework.
"She's fascinated by me because I'm from this neighborhood and I went to college," Cooper said. "She respects me even when she doesn't respect her teachers."
Since she started the one-on-one sessions, Cooper said she's noticed that the girl has been getting better grades.
"Her behavior is still a little shaky, but she's now doing her work [consistently]," Cooper said.
* As for parent Colleen McAllister, whose third-grader attends the high-achieving Kearney School, 6th Street near Fairmount Avenue, in Northern Liberties, making the job of the teacher easier is her way of giving back.
"It's important for parents to be active," she said.
She said she no longer reads to first-graders as she used to, but sits on a committee with the principal, teachers and other parents discussing school policies and budgetary matters.
She also chaperones field trips and organizes fundraisers.
"These teachers are like social workers and parents," she said. "And to help them out in any way I can is wonderful."