BAGHDAD — A suicide bomber pushing an electric heater atop a cart packed with hidden explosives attacked a high school north of Baghdad on yesterday, leaving students and teachers bloodied and bewildered as insurgents appeared to be expanding their list of targets.

The bombing — one of two attacks near Iraqi schools on the same day — follows a wave of recent blasts blamed on Al Qaeda in Iraq against funerals and social gatherings.

The trend points to the possibility that Al Qaeda has shifted tactics to focus increasingly on so-called soft targets and undermine public confidence that things are looking better in the country. The backlash also coincides with an American-led offensive trying to uproot insurgents from strongholds around Baghdad.

In the suicide attack, the bomber posed as a shopper or merchant transporting an electric heater on a chilly winter day — an apparent attempt to deflect attention from the explosive-rigged cart.

The blast struck the front of a two-story schoolhouse in Baqouba about 8:30 a.m., half an hour after classes began. Panicked parents rushed to find out if their children were alive or dead.

A 25-year-old male bystander was killed and 21 people were wounded — 12 students, eight teachers, and one policeman, according to a doctor at Baqouba General Hospital who spoke on condition of anonymity because he was afraid of being targeted by militants.

“I can’t think of any reason to target students,” a 15-year-old, Mohammed Abbas, said, his wounded head in a bandage as his father stood near his hospital bed in Baqouba, about 35 miles northeast of Baghdad. “We did not expect that explosions would reach our school.”

In the other attack, a roadside bomb exploded next to a girl’s high school in Baghdad’s western district of Amiriyah, wounding a 7-year-old boy who was passing by. But police said the target was an American patrol, not the school.

Insurgents appear to be looking for ways to bypass the heavy security cordons and patrols that cover any major event or site.

The Associated Press also reported that a top American military commander in Iraq said yesterday that troops have Al Qaeda on the run but will never completely be finished chasing them “because they may always come back.”

A Major General in the Army and commander of coalition forces in northern Iraq, Mark Hertling, said some 40 military operations in his area since the last week of December have killed more than 130 militants and netted more than 370 prisoners, including 40 so-called “high-value individuals.”