A collective shudder ran through America again on Monday as news broke that a 15-year-old allegedly shot 15 people at a California high school, killing two.

The shooting echoed the deadly 1999 rampage at Columbine High School in Colorado, where two teenagers shot and killed 12 people before committing suicide.

As details of Monday’s attack unraveled, a concerning thread arose: The shooter had warned -&160;even bragged – of his plans to both peers and adults. And no one took his threats seriously.

We have to wonder what might have happened if someone had chosen to report the threats – to police or law enforcement authorities; to the boy’s father; to anyone else.

We can no longer dismiss threats of violence and rampage from our teens.

We have learned that painful lesson in places like Columbine, and now Santee, Calif.

And we have paid a dear price for that lesson.

No matter the reason – lack of strong families, exposure to excessive violence in popular culture, easy access to weapons, inability to cope with the challenges of adolescence – adults will cite, we can control only our role in the situation.

It doesn’t matter the reason, the reality is our children are on the brink, and we all need to be responsible adults when they send out cries for help.

As an acquaintance of the California shooter was quoted by the Associated Press as saying, &uot;I should’ve stepped up even if it wasn’t true … to take that precaution.&uot;

Unfortunately, he’s right.