As the Celtics honored hundreds of middle school students for their perfect attendance at Thursday’s 22nd annual “Stay in School” celebration at Northeastern University, Jared Sullinger shared the lessons he’s learned since undergoing the surgery to repair a lumbar disk that ended his rookie season in February. “In life, it’s kind of different,” said the recently turned 21-year-old power forward. “Teachers give you a lesson and then the test whereas in life you get the test and then the lesson. I’ve learned that through this situation right now. I’m getting a test of my patience, my discipline … so I’m just learning the lesson now.” The lesson in patience should be completed by the end of the summer. By his calculations, Sullinger’s 50 percent and on target to return fully healthy before training camp. “It’s a 10-week process,” said Sullinger. “Every two weeks, we’re going to bump it up 10 percent. By September or October, I’ll be 100 percent to go full. About two weeks ago, I met with the doctor. He said it’s a full go. Our medical staff — [strength and conditioning coach] Bryan Doo, [head trainer] Ed Lacerte — we’re just taking it slow. You don’t want to go right into the pounding, so every two weeks it’s just 10 percent bumping it up.” Sullinger averaged 6.0 points and 5.9 rebounds in 19.8 minutes a night over 45 games as a rookie, eventually earning high praise from his teammates for his basketball IQ and a starting role in late January. When he does finally play for the first time since aggravating the injury four minutes into a game against the Kings on Jan. 30, he’s been told the medical issue that’s plagued him since his Ohio State days will be gone. “Everybody says back with a question mark,” said Sullinger, “but you might as well put an X through that, because I had surgery, I’m taking my time and getting back right. There won’t be a reoccurring injury.” As a precaution, Sullinger will not participate in the Orlando summer league this July, but at least the long months of sitting around watching movies, playing video games and analyzing clips of his game are over.