About 450 children walk up the steps to CornerHouse in Minneapolis each year and describe to staff members inside how they’ve been physically or sexually abused.

Recorded on closed-circuit TV, each interview is monitored by staff from law enforcement, child protection and the county attorney’s office, and is conducted in such a way that it is permissible as court evidence.

The unusual nonprofit marks its 25th anniversary this year as one of Minnesota’s first such child advocacy agencies, assessing children for suspected abuse, conducting “forensic interviews” and teaching professionals across the nation how to interview these fragile children.

“Our goal is to make sure the voices of children are heard,” said Patricia Harmon, executive director of the CornerHouse Interagency Child Abuse Evaluation & Training Center.

Minnesota child-protection workers assessed 18,284 reports of child maltreatment in 2012 involving 25,839 children, according to state figures. Not all were opened for investigation.

CornerHouse developed a protocol for interviewing abused children using techniques that reflect the child’s development stage, as well as provide admissible evidence in court, said Harmon. Before this, abused children were often interviewed multiple times, sometimes changing their stories to reflect whom they were talking to.

“People didn’t realize child development issues, such as how a child responds to an interview with law enforcement carrying a gun,” she said.

Over the past 25 years, CornerHouse has trained 26,000 professionals from every state to do the same, she said. Working with other similar agencies, it has contributed to a body of “best practices” that now guide the interview process across the country and other nations.

Its funders include the Anchor Bank Family Foundation of Wayzata, the Staley Family Foundation of Pennsylvania and many private businesses such as Parsons Electric in Fridley, according to center reports. To learn more, go to www.cornerhousemn.org.