But Terre wouldn't be there.
On July 27, the 17-year-old was shot to death on an East Germantown playground, one of four victims caught in gunfire when police believe a drug dealer, trying to rob people, sprayed bullets. His death came just hours before Mayor Street took to the airwaves, calling for an end to the violence that has sent the city's homicide rate climbing.
Terre's death shocked and horrified his classmates, who kept his desk empty all year, and whose studies of peace took on greater meaning than they could have imagined.
In her grief, Washington found some solace. A worker for the Philadelphia School District told her Terre would get a diploma.
Then, a couple of weeks ago, the district said that because Terre died during the summer, before starting 12th grade, he couldn't get a diploma after all. Instead, there would be a certificate of some kind.
As she walked to the subway, Washington was caught up in a swirl of emotions:
Excitement about the prospect of a graduate's winning the $500 scholarship her family had raised for a student who had overcome adversity.
Nervousness about possibly having to go up on the stage.
Anger about the denial of the diploma, which would have meant "that a part of him is here."
Shortly before 3 p.m., Washington arrived at the graduation site - New Covenant Church at 7500 Germantown Ave., on the same campus as the school - with her daughters, Rhonda Washington, 34, and Tasha James, 27; Tasha's son and daughter; and two little cousins. They took seats near the back.
The seniors marched in, wearing bright red gowns and caps. The faculty marched in. There were songs, the Pledge of Allegiance, a welcome, speeches, and more music.
Then Marquis Herring, a senior class speaker, went to the lectern.
"What's amazing is that we've accomplished so much this year alone, even with this heavy pain in our hearts," he said, and then talked about Terre.
"We argued and lashed out at anything and anyone that was close to us, trying to make sense of the reasons as to why this happened to them," he said of Terre and a beloved school police officer who died after surgery.
"We laughed for all the good times we shared with them . . . like when Terrence would break wind in American history class and blame it on everybody in the back row of the classroom."
The audience laughed.
"Terrence could always make you laugh, even if you were mad at the whole world."
Washington hid her face in her hands, overwhelmed. Tears rolled down daughter Rhonda's cheeks.
Cousin Jasir Lightfoot, 7, known as "Little Terre" - they were so close - sobbed. He leaned his head against Tasha, who cradled him in her arm. Tasha's daughter, Tatyana, 7, cried, too. For a while, she didn't want to go back to Pastorius School because Terre died on that playground. Tasha's son, Tamir, 5, wearing a shirt with Terre's picture, looked confused.
A staff member rose to read the names of the students who scored highest on state tests. Terre's name was read. He had wanted to be a graphic artist and had scored high in math.
One of Terre's best friends, Ni'mat Guyton, was praised for his proficiency in reading, math and writing.
"Yeah, Ni'mat!" Washington yelled.
Then principal Ethyl McGee stepped to the podium.
"At this time, I'm going to ask the mother of Terrence Adams to come forward," McGee said.
Almost automatically, Washington stood. "I'm going to try to get through this," she whispered to Rhonda as she made her way to the stage.
Washington leaned on the lectern, cupping her chin in her hand, doing all she could to hold herself up. McGee asked if she wanted to speak. Washington shook her head.
McGee called Terre a "courteous, kind, friendly" young man. His death, she told the audience, "makes no sense. None of the deaths really make sense. But he was not out doing harm to anyone, but harm came to him."
Then she announced the scholarship winner: It was Marquis Herring, whose family was thrust into homelessness last year. The young playwright will study theater at Lock Haven University.
Months ago, for Terre's memorial, Marquis had drawn a picture of his friend, with wings, flying to heaven.
McGee turned to Washington and handed her flowers, a yearbook, and a certificate of achievement for Terre. The audience stood and clapped.
Terre's classmates should sign the yearbook, Rhonda told her mother as she sat down. "I don't think I feel like dealing with them yet," Washington replied.
"Well, this is part of the process," Rhonda said.
As the graduates poured out of the hall amid celebratory whoops, Washington saw Ni'mat. "Can I get you all to sign Terre's yearbook?" she asked, hugging him.
Ni'mat took a pen: "RIP Boathead! We made it!!"
Washington spotted Marquis. "The Lord tells me I have many sons, but thank you for being one," she said.
Still, she wished Terre had gotten a diploma. "I love Mrs. McGee. She did everything she could to accommodate me."
Ni'mat and several other friends wanted to make sure Terre got a diploma, and decided to put a copy of one of theirs on his grave. But they feared it would blow away.
Instead, they planned to visit Terre's grave today - which would have been his 18th birthday - and give a copy of Ni'mat's diploma to Washington. But before they could make their pilgrimage, Washington learned that Terre would get a diploma of his own.
Late yesterday afternoon, school district officials said they had reviewed their policy and would issue an honorary diploma for Terre.
Hearing the news, Washington screamed: "I am just ecstatic! Now, I am complete!"
View a slide show about Terre Adams' family, and what should have been his high school graduation, at http://go.philly.com/terre.
Contact staff writer Susan Snyder at 215-854-4693 or firstname.lastname@example.org.