U.S. authorities say a 29-year-old convicted sex offender was able to pass as a 12-year-old boy in seventh grade for four months at a school in Arizona last year.

Neil Havens Rodreick II, a convicted sex offender from Oklahoma, spent a total of 50 days in class at the Imagine Charter School in Surprise, a suburb about 32 kilometres northwest of Phoenix.

Neil Havens Rodreick II, 29, a convicted sex offender from Oklahoma, allegedly shaved his body and used makeup to cover his stubble while posing as a Grade 7 student in Arizona.
(Yavapai County Sheriff/Associated Press)

School officials expelled him for poor attendance in 2006.

Rodreick, five feet eight inches tall and weighing about 120 pounds, is believed to have shaved his body hair, used makeup to cover his stubble and adopted a new name to pose as a boy. He was known as Casey Price.

Police arrested him on Jan. 18, a day after he tried to enrol at a school in Chino Valley, about 145 kilometres northwest of Phoenix, as a seventh grader.

Rodreick is facing a number of charges, including conspiracy to commit fraud, conspiracy to commit forgery and failing to register as a sex offender.

He served seven years in jail in Oklahoma after being convicted of making lewd and indecent proposals to a six-year-old boy in 1996.

"He absolutely looked age-appropriate, " Rhonda Cagle, a spokesperson for Imagine Charter School, told the New York Times in an article published Thursday.

"We have several seventh-grade students who are taller and of a larger build than this individual."

Cagle said teachers have told her that he was a quiet student and completed his homework on time, but did not take part in after-school activities.

Parents, however, told the New York Times that they are stunned by the news.

"Obviously, there are a lot of emotions to work through," Mindy Newlin, a parent of a kindergarten student at Imagine, was quoted as saying by the New York Times. "We are just shocked."

Rodreick lived with three other men who posed as his uncle, grandfather and cousin. The men, who are facing a number of charges as well, were convinced by Rodreick to act as his relatives, according to the newspaper.

U.S. authorities say Rodreick spent close to two years in all posing as a minor. Authorities told the New York Times that he is being investigated in three American states.

With files from the Associated Press