Frank Somerville, a journalist at KTVU in California shared the image on Facebook after being sent it from one of the youngsters' mothers along with a note.
Noelle Smith was quoted as saying: "I want to share a picture of my daughter and her friends from prom night.
"Now with the stories today about teenagers and tide pods and condoms gathering headlines - this picture speaks for itself.
"They all said Grace before eating and were all well behaved."
However, the post which attracted more than 500 comments irked some people.
One user felt insulted and said: "So if I don't say grace but open doors for people, use crosswalks, obey all laws etc I'm not a good person GET REAL."
While another said: "No offense, but saying grace doesn't mean any of those things. I've known people who do exactly this kind of stuff in public, but who are the most hypocritical, hateful jerks in private.
"Not saying these kids are like that, but just assuming they're great based on this is a) taking quite a leap and b) kind of implying people who don't believe can't possibly be on the same level."
Somerville said he was "honestly surprised" by the comments and defended sharing the picture: "I wasn't trying to imply that you have to be a Christian to be a good person,
"What I see from these kids is that they are respectful...they are humbled...and that they are appreciative for what they have. ... I could care less whether they are religious....but by saying grace it shows me that they have those qualities...and those are the qualities... regardless of whether you believe in God ... that I admire."
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