The principal of Middle School Virtual Academy said Friday's disruption was caused by four or five students who were not supposed to be there.
Parent Kathleen Sarpy said her 12-year-old son was in that class and alerted her to what happened.
"He goes, 'Mom, there were naked people on the screen,'" Sarpy said. "It was shocking and upsetting, to put it mildly... Honestly, I felt like his innocence was lost. I was really devastated."
In an email to parents, the principal said the substitute teacher was not aware that those individuals aren't normally in the class.
He said the IT department is now working to identify them and promising "appropriate consequences" for "everyone who was involved."