Seniors at San Pedro High School, where graduation ceremonies ended abruptly last week when administrators and teachers walked out because of rowdyism, staged a replay of their own. "We had a turnout of almost 200 students and their parents, about 500 or 600 people altogether," said Doug Kato, one of two student body presidents. The repeat performance at a San Pedro Park featured speeches that the class valedictorian and salutatorian never got to give. Students, wearing caps but not gowns, also got to walk to the podium as their names were called. Regular graduation ceremonies for more than 560 seniors were cut short because boisterous students were participating in the wave--alternately standing and sitting--shouting, and bouncing beach balls through the crowd. Kato said students behaved maturely and solemnly at the repeat ceremonies, but they did perform the wave three times at the end.