But if Blackman had lived in at least a half-dozen other states, his name would never have appeared on a registry because states are deeply divided on how to deal with America's youngest sex offenders.
Juvenile justice advocates want rehabilitation instead of registration, yet public safety experts argue children must be protected from predators, even if they are minors.
The confusing array of rules for juvenile sex offenders persists despite a vast overhaul that was adopted four years ago to bring clarity and consistency to U.S. sex offender regristration laws.
"It's a real bind for the states," said Michele Deitch, an attorney who teaches criminal justice policy at the University of Texas.
"Do you want to comply with what could be poor public policy or risk not complying with the federal law? And there's no easy answer."
Twenty-one states currently require juveniles convicted of a serious sex crime to register with law enforcement, according to an Associated Press review of state laws and interviews with state officials.
In 19 other states, only juveniles convicted as adults or who move from a state that requires registration are required to provide their information to authorities. In the remaining states, the laws vary. In Nevada, for instance, a juvenile sex offender can petition a judge to set aside registration requirements.
Lag to Comply with Bush-Era Law
In 2006, President George W. Bush signed a law requiring states to adopt a series of sex offender measures, including the registration of all juveniles who commit serious sex crimes such as abuse or rape. The law was designed to create a national sex offender registry and toughen penalties for those who fail to register.
Ohio is so far the only state to meet the new federal standards, but states have until July to comply so they can build up their online registries and ensure the information can be incorporated into the national database.
Of the 21 states that require juvenile sex offenders to register, at least four states do not publish all of their details online, such as photographs and home addresses.
Critics said young offenders will be more likely to reoffend because of the humiliation of being labeled a sex offender.
"These kids can get better and here you are punishing them for life without offering any treatment. That to me is unethical," said Dr. Valerie Arnold, the interim chief of child and adolescent psychiatry at the University of Tennessee. "Even convicted murderers aren't put on a list like this."
It's unclear how many of the estimated 686,000 sex offenders in the United States are juveniles. But a recent study by the University of New Hampshire Crimes against Children Research Center that found more than a third of those who sexually abuse children are juveniles.
"It's a difficult balance," said Ernie Allen of the National Center for Missing and Exploited Children. "We're in favor of the rehabilitative ideal and targeting treatment for the youngest offenders, but many of America's offenders are kids and they are committing very serious sex offenses."
The stress of being listed on a public registry can be overwhelming for young sex offenders.
In Blackman's case, his family later moved to Oklahoma, where he was also required to register. After his name was posted, Blackman said he was kicked out of school and neighbors began harassing his family.
One neighbor followed him with a video camera and insisted the family move, and they eventually decided to resettle in a rural area to escape the scrutiny.
"I was really depressed and I was always stressed out," said Blackman, now 21. "It changed me. I lost a lot of my childhood and now I have a lot of catching up to do."
Even though his record was expunged, his name stayed on the list until his mother lobbied state lawmakers to change the law. Blackman has since been removed from the registry.
Yet he says he still suffers with the stigma reluctant to go to the park, watch his little brother's basketball games or be alone with his cousin's infant fearing his actions could be misconstrued.
"It's sad. He's 21 now and there's so much damage that's been done to him," said Blackman's mother, Mary Duval. "All he wants is his life back but he doesn't know if it's going to happen."
Those who want juvenile sex offenders on registries acknowledge the requirements are not ideal, but they say the benefits to public safety far outweigh the impact on a juvenile sex offender's psyche.
Supporters often refer to the case of Amie Zyla, who was sexually assaulted when she was 8 years old in Wisconsin by a 14-year-old family friend. She became a leading advocate of juvenile registration requirements when her perpetrator was sentenced to 25 years in prison after pleading guilty to later fondling two teen boys.
"The simple truth is that juvenile sex offenders turn into adult predators," she said at a 2005 Congressional hearing. "Kids all over the country need the same kind of protection as in Wisconsin."
Treatment Differs by State
Yet there is a wide disparity in how states treat juvenile offenders.
In Texas, where judges decide whether to put juveniles on the registry, lawmakers led a push several years ago to make it automatic. But the measure's sponsor, Texas state Rep. Jim McReynolds, said he abandoned the effort after concluding the new requirements would be too costly and may end up harming the juvenile offenders.
"The more I began to look at it, the more I saw it was pretty doggone tough on juveniles," said McReynolds, who chairs the House Corrections Committee. He now favors more treatment.
In Maryland, powerful lawmakers are aiming to require those 14 and older who commit rape and other serious sex crimes to register.
"Juveniles are treated as adults in other areas of the law," said Delegate Bill Frank of Baltimore County, one of the measure's sponsors. "And if a juvenile commits a first-degree rape, that juvenile should be required to register as a sexual offender."