DeJong, 31, began Friday classes with a riddle and sometimes played pranks on other teachers. At least once, he set off a bottle rocket outside during a chemistry class.
"He always seemed to be ready for a joke," said Brennan Macaster, an El Cerrito High junior who had DeJong as a chemistry teacher last year. "Inside he was probably about 6. He seemed more like a student sometimes."
DeJong's energy made his recent death all the more shocking.
Family, students, parents and teachers this week are mourning DeJong, who died mysteriously the Tuesday or Wednesday before Thanksgiving. The Contra Costa County Coroner's Office has not determined a cause of death, said DeJong's mother, Kathi DeJong.
Kathi DeJong said her son failed to show for the family's holiday celebration, and a family member who went to check on him discovered him in his El Cerrito home . There were no visible indicators of death, she said, adding that he did have some health problems that might have played a part. She would not elaborate.
"I'm kind of falling apart at the seams," Kathi DeJong said Tuesday. "We were expecting him to show up, and he didn't show up."
DeJong's death also upset the El Cerrito High community, which learned the news when school resumed Monday.
"It's really surprising, and I don't think it's hit me yet," said junior Liana Miles, who was in DeJong's chemistry class last year. "I think I have to walk by his classroom and see it empty to believe he's gone."
DeJong, who started his teaching career in the Berkeley Unified School District, was in the middle of his third year at El Cerrito High. He and his wife, Christine Yang, were married for eight years. Yang did not return a call seeking comment.
DeJong worked long hours as a chemistry teacher but last year took on more responsibility as the director of the school's much-lauded drama department. He oversaw last year's production of "Baby in the Bath Water" and this year's production of "Antigone."
"He loved theater and was so proud of teaching chemistry," Kathi DeJong said. "He loved his job."
Many students loved him, too. Several gathered outside school Tuesday afternoon and traded stories, talking about the famous "chemi" awards in which DeJong gave out little vial statuettes to students that read things such as "class clown" as voted on by the class.
"He made chemistry seem fun with the way he presented it," said junior Yolini Banerjee, whom DeJong chaperoned in the summer during a trip to Brown University. "He was a teacher who understood things if you came to ask him for help. He was a people person."
West Contra Costa Unified School District officials provided El Cerrito High with extra grievance counselors this week to talk with students and staff, El Cerrito High Principal Jason Reimann said.
"It's very difficult for students to adjust," Reimann said. "For many of them, this is the first time they've lost people who are close to them. On the whole, I've been impressed with the students' resilience."
Reimann said the school plans to hold some type of memorial service to honor DeJong but is awaiting word from his family before finalizing a time and place.
A public memorial service and memorial fund in which donations will be made to the El Cerrito High drama department are being set up, Kathi DeJong said.
"We're thinking of Mr. DeJong's family right now," Reimann said. "He's touched a lot of lives."
Reach Kimberly S. Wetzel at 510-262-2798 or firstname.lastname@example.org.