Students across New Hampshire returned to schools on Monday, many of their minds gripped by the mass killings Friday at a Connecticut elementary school.

Police were out in force in some schools and school areas, and one high school went into lockdown when an assistant principal heard a loud noise he couldn't explain. But at other schools, principals said few students mentioned the Sandy Hook Elementary School tragedy, and those who did so spoke in generalities or whispers.

"Either parents had great conversations this weekend or kids didn't see anything (in newspapers or television) at all," said Richard Norton, principal of Green Acres Elementary School in Manchester.

A loud noise in Windham High School - possibly a falling wrestling mat - prompted officials to call police, place students in lockdown, and search the school from top to bottom. Police said they found nothing out of the ordinary, and school officials said they can't explain what caused the noise.

One student, Ram Sheth, said he thinks it was a prank.

"The person who did that isn't the smartest person," Sheth said. "You don't do that after what happened (in Connecticut)."

Mixed moring precipitation prompted officials across southern New Hampshire to delay the start of many schools. That gave parents a little extra time with their children Monday morning, said Webster Elementary Principal Christine Martin.

It also gave her a chance to have a pep talk with her teachers. Martin told teachers she believed they would have reacted just as those at Sandy Hook Elementary. Likewise, Webster teachers told Martin she would have done the same as the principal.

Sandy Hook Principal Dawn Hochsprung and several faculty died in the killing spree.

Martin said only a couple of fourth graders spoke to teachers about Sandy Hook, doing so in generalities. Teachers acknowledged the fears or sadness on the part of students but assured them they were safe, Martin said. ?"That's really all the kids wanted. They needed to hear it for themselves," Martin said.

Others schools opted for students to see it for themselves. In Derry and Goffstown, police made a heightened presence at schools and school zones.

"Providing a sense of normalcy would be extremely difficult, but providing a feeling of safety is most important," said Goffstown police Capt. Robert Browne, whose department had all available police patrol school zones in the morning and afternoon. Police also conducted extra walk-throughs of school buildings.

At Peter Woodbury Elementary School in Bedford, Principal Kenneth Williams said teachers maintained a routine for students. For younger students, the repeated a simple message - they are safe.

"Our big thing is to be very visible, give hugs and be there for kids if they're having trouble with the incident," Williams said.

The jolt at Windham took place about 10:30 a.m., when an assistant principal heard a loud noise. Sheth said students were herded into the nearest classroom and told to stay in place. Sheth said everyone is familiar with the procedures because they drill about once a month.

"Windham's generally a pretty safe town," he said.

Colleen Cooney, a Windham senior, said she felt unnerved by the incident. She said the noise was caused by a falling mat.

Interim Windham Superintendent Henry E. LaBranche said officials don't know what caused the sound. He said the school sent an alert to parents after the lockdown was concluded. He said the Connecticut shooting provided added weight to the decision to lockdown and sweep the school.

"We're pretty diligent about enforcing our safety regulations and emergency plans," he said.

Meanwhile, Green Acre's Norton said that Monday would have been the day for students to get upset over Sandy Hook. For the rest of the week, class parties and school concerts take hold.

"There'll be such a distraction; the fall out would have been today," he said.

mhayward@unionleader.com

Correspondents Kathy Remillard, April Guilment and Adam Swift contributed to this article.