Inspired by @list
  1. Gym class was held in a location other than the school building and I would have to take a bus to get there. (Age 5)
  2. Fig Newton filling contained squished-up flies. Also, raisins were probably squished-up flies. (Age 6 or 7)
    This was a popular rumor around my school. I mostly knew it wasn't true, but having never had a real fig, I couldn't account for the crunchy bits. Flies seemed like a fairly reasonable explanation.
  3. "Penalize" was a bad word (because it sounded like penis). (Age 8-ish)
    I remember hearing my parents use it in conversation as we were driving one day and feeling mortified that they were discussing it so openly.
  4. Conscious and conscience were both spelled "conscience" and just meant two different things. I even insisted as much to my 5th grade teacher. (Age 10)
    For the record, she was also anti-Oxford comma, so I was skeptical of her authority.
  5. Yellow gold was what rich people had and silver colored jewelry was only worn if you couldn't afford the good stuff. (Embarrassingly, until age 16 or so.)
    We didn't have much money, so my assumptions were based on Macy's ads from the newspaper and what my "rich" grandmother wore.