When my kids were in school around 15 years ago, the health teacher decided to show a sex film the last week of school and sent a notice the home the day before. I was so proud of my daughter who immediately said to him in class "I opt out". He said I'm not sure you can do that. I called and spoke with him and he said I could preview the film with my child when they show it in the classroom if I wanted. I said my daughter is opting out so appropriate accommodation needed to be made, and berated him for stealthily trying to get this in under the radar at the last minute, not giving adequate notice and reminded him that the definition of preview is to show before the regular viewing, not during the regular viewing. He was taken aback but caved to my insistence. So even back then, teachers were trying to hide their shenanigans.
It was incompetence either way.