Spc. Nicholas P. Olson, 22, died after an improvised explosive device detonated near his unit in Muqdadiya, a city northeast of Baghdad, the Defense Department said. No additional details about the incident were released.

Flags at Novato High School and Marin Oaks High School were flown at half-staff on Thursday to remember Olson, who leaves behind a wife and 10-month-old daughter, said Novato High School Assistant Principal Dan Curtaz.

Curtaz, who was Olson's physical-education teacher when Olson was a freshman, called his former student "a young man with a lot of energy. He was a good kid."

During his years at Novato High School, Olson was enrolled in its junior ROTC program, and always wore his uniform with pride, said Curtaz.

"Those uniforms have to be tucked in in a certain way, nice and neat, and he definitely respected it in the right way," Curtaz said.

Olson attended Novato High School until his senior year before transferring to Marin Oaks, a continuation high school, Curtaz said. Olson left Marin Oaks in 2003, said Kathy Marshall, the Novato Unified School District's executive director of curriculum and instruction.

Olson enlisted in the Army in October 2004 and was assigned to the 4th Brigade, 2nd Infantry Division, known as the Stryker Brigade Combat team, out of Fort Lewis, Wash. Olson's brigade had been in Iraq since April, the Army said.

During his Army career, Olson was decorated with the Army Achievement Medal, the National Defense Service Medal, Global War on Terrorism Service Medal and the Army Service Ribbon.

On Thursday, students at Novato High School looked at a yearbook featuring Olson's photo, said Curtaz, who made the school announcement of Olson's death. He says Olson's death is the first of a former Novato student in the Iraq war. Olson's wife, Nicole, also attended Novato High School, said Curtaz.

"It definitely hits close to home," said Curtaz, 35, who has spent most of his life in the northern Marin County city. "Now, it's one of our own. Before, it's always been someone from Santa Rosa, San Francisco, and other places. This has made everyone here think a little bit more. It's something that's affected the entire student body. Some students have older brothers and sisters who knew him."

Also killed in the explosion that killed Olson were Spc. Joseph N. Landry III, 23, of Pensacola, Fla., and Spc. Donald E. Valentine III, 21, of Orange Park, Fla.

E-mail the writers at jcuriel@sfchronicle.com and mlagos@sfchronicle.com.

This article appeared on page B - 2 of the San Francisco Chronicle