In West Hartford, Superintendent Karen List sent a recorded message to families Friday noting an increased police presence at town schools after the Newtown shootings.

“It’s really for reassurance,” List said. Counselors will also be available for students at the schools, and West Hartford administrators are now creating a set of talking points for parents if they decide to explain the shootings to their children over the weekend.

A meeting of Farmington Valley-area superintendents that was scheduled for Friday was canceled.

“We need to be in our districts,” List said. “We need to be communicating with our families; we need to be supporting our faculty and children.”

Southington schools were placed on a precautionary “passive lockdown” in which exterior doors are locked, Assistant Superintendent Karen Smith said. “We’re asking all administrators to be vigilant and to be aware of what is going on.”

In Waterbury, Wilby, Crosby and Kennedy high schools have canceled Friday’s afternoon and night games, according to the school system. Other after-school activities for Waterbury schools will go on as planned, but there will be police on the premises.

Bridgeport Superintendant of Schools Paul G. Vallas has canceled all after-school programs except for the Central High School basketball game.  

All Winterfest Hartford activities in Bushnell Park in Hartford will be closed today. The skating rink is closed effective immediately and will re-open tomorrow on regular schedule.

Schools in the Pomperaug Regional School District 15, based in nearby Southbury and Middlebury, were put on lockdown after the shootings, Superintendent Frank Sippy said. After-school and weekend activities were canceled.

“Everyone is searching for the reason why — why such a senseless tragedy has to transpire in this country,” Sippy said.

“We’ll take the weekend to reflect. I just think it’s time for people to step back and take a breath and spend time with loved ones,” said Sippy, who has offered the district’s services to Newtown schools. 

The only mass shooting in the U.S. with more than 27 killed since the 1950s took place on April 16, 2007, when a student named Seung-Hui Cho shot and killed 32 people at Virginia Tech in Blackburg, Va., before shooting himself.

On May 18, 1927, Andrew Kehoe, school board treasurer in Bath Township, Michigan, bombed three schools, killing 38 children, two teachers and four other adults, as well as himself, because he was enraged by higher taxes to fund a new school.

Friday’s massacre may be the largest school shooting of young children in the world, said Larry Barton, a professor at the American College in Pennsylvania whose three decades of research includes studying violence in workplaces, public spaces and schools.

Mass school shootings have often targeted high schoolers, such as the victims of Columbine, and university-age students. And in China, there have been numerous cases over the past three years of knife-wielding adults attacking children, such as an incident Friday in the Henan province where a man slashed 22 children.

“This is among the most diabolical crimes, to kill kindergarten-age children,” Barton said of the Newtown case. “It’s very rare.”

Barton also teaches threat assessment at the FBI Academy in Quantico, Va., where one of the cases he presents to law enforcement is the 2010 Hartford Distributors Inc. rampage in Manchester. Omar Thornton, 34, fatally shot eight of his co-workers before killing himself.

“The most dangerous person in society is what we call the grievance collector,” Barton said. “It’s the person who has a grudge, who cannot let go of an issue. They become obsessed and they tend to be exceptional at both planning and documenting ...

“It will take weeks, maybe even months, to understand motivation. Often what the shooter is seeking is not just revenge, but notoriety,” Barton said. “They are seeking a sense of trying to eclipse prior perpetrators.”

- Staff writers David Owens, Dave Altimari, Josh Kovner, Marc O'Connell, Chris Keating, Samaia Hernandez, Denise Buffa, Steve Goode, Brian Dowling, Hilda Munoz, Jenny Wilson, Vanessa de la Torre, Jenna Carlesso, Bernie Davidow, Naedine Hazell, Sandy Csizmar and Stephen Busemeyer contributed to this report. Associated Press reports are included.