Julie Amero, a substitute teacher at a middle school in Norwich, Conn., said she had simply wanted to e-mail her husband. The authorities contend that she was  purposely or, perhaps, carelessly  exposing 11- and 12-year-old students to pornography rather than teaching them English.

Last month, Ms. Amero was convicted in Norwich Superior Court of four counts of risking injury to a child and faces up to 40 years in prison at a sentencing hearing scheduled for March 2. She has insisted on her innocence, refusing to accept a plea bargain that would have allowed her to walk free. She portrays herself as a hapless technophobe too clueless to unplug a wayward computer.

Ms. Amero, 40, a longtime substitute, contends that when she arrived that day in October 2004, she asked the regular seventh-grade language arts teacher at Kelly Middle School if she could use his computer to e-mail her husband. But first, she says, she went to the bathroom, and when she returned, the teacher was gone and students were gathered around the screen, watching a hairstyle Web site.

When she tried to close the site, what she got was an endless barrage of pop-up ads for pornography sites. The images continued all day, since “I absolutely have no clue about computers,” she said in an interview.