KALISPELL, Mont. -

Flathead authorities say a 26-year old convicted sex offender failed to register his new address, and then it was learned he was working at a Kalispell ballet school. The owner of the Northwest Ballet School and Company says Donald Stanfield was hired to teach a class in 2011, a few years after he pleaded guilty to a charge of sexual assault, though she says she wasn?t aware of his history.

Marisa Roth tells NBC Montana she didn?t have any reason to be suspicious of Stanfield after working closely with him over the years. She says he started dancing in some of the school?s performances back in 2006, before his conviction. Roth says her company didn?t run a background check on him before they hired him to teach. One parent NBC Montana spoke with said she doubts the company would knowingly hire a sex offender. She also said a background check should be standard.

?Hindsight is 20-20,? said Marci Mangold. ?When you have somebody working with small children you should always do a background check, just to be sure about things, but as a parent I feel responsible for my own kids and so I?m not going to leave them unattended at their dance classes if I don?t feel 100 percent safe with those instructors.?

Roth tells NBC Montana Stanfield was fired from the company, and that the company has started a policy to do background checks on staff members who interact with kids.