CBS News correspondent Jim Axelrod reported three seniors at Concord High School -- plus a drop out -- face charges in what police say was an especially cruel episode of bullying.
Principal Gene Connolly told reporters, "This is by far, (in) my 30 years as an educator, the worst event that I've ever had to deal with."
Police say the classmates told the victim they'd stop picking on him if he let them tattoo the image on his rear end. Three of the suspects allegedly tattooed him with their own needles.
The mother of one of them says the boys acted stupidly, but not maliciously.
Patti VanNest said, "They told me about it. They were joking about it. They thought it was something funny. And I believe there wasn't any animosity or hatred."
Police were called when a teacher saw some students passing around photos of the tattoo.
Connolly said, "Folks been using the word bullying. I almost think it's more horrific than bullying."
The charges include assault, endangering the welfare of a minor and indecent exposure. If convicted, the four suspects are looking at sentences ranging from three to 13 years.
Child and adolescent psychologist Dr. Jennifer Hartstein said on "The Early Show" Tuesday that children with special needs, such as the one in this case, are especially vulnerable.
"These kids want to be included, they want to participate, they want to be part of the crowd. And now all freshmen want to be part of the crowd. But then add a cognitive limitation in there, and there's even more. So he was especially vulnerable to want to be part of these older kids, 17, 18, 19, 20-year-old kids wanted to befriend him, how great, how cool. So he worked really hard to do whatever it was that they might want. And ultimately this was the horrible consequence."
She continued, "And who is protecting the kids, the younger kids? Kids are entitled to an education until they're 21, so there are going to be schools where you'll have 20-year-olds with 13 and 14-year-olds. So who is protecting the younger kids and who is protecting the kids who are more vulnerable or have cognitive limitations?"
So is this bullying -- or something even worse?
Hartstein said, "It's bullying taken a step further, especially because you're dealing with some young men who are adults. In the eyes of the law, 18, 19, 20, they're adults. So now you're taking it to a different level. But at the end of the day, it's almost really traditional bullying, really, 'You do this, you will be our friend.' And that's just what it came down to."