The bells rang out as names of each of the victims were read at St. Rose of Lima church in Newtown, one of several houses of worship that held private services for a community still grieving the deaths of 20 children and six educators.
President Barack Obama and the first lady held a moment of silence and lit 26 candles at the White House to remember the victims killed at the school.
One year ago, Adam Lanza killed his mother and then drove to the school where he carried out his rampage. He killed himself as police arrived.
Newtown officials and victims' families are calling for people to mark the anniversary by performing acts of kindness or volunteering with charities.
The Associated Press contributed to this report.