I once randomly thought out loud that school days were 14 hours long, only to find out that it's actually 6. No idea why.
A childhood belief about classes

others believed things like this
- I thought that days had 100 hours in them. Very surprised to hear there were only 24.— Cassiopeia
- When I was in elementary school I use to think that teacher lived at school at their desks all year long.Anon
- In kindergarden my friend told me that there were 24 hours in the day and 15 hours in the night.— Cari
- I thought farting was magical wind, and if you did it loud and hard, you would be able to move yourself.— Blake
- I used to believe that when I went to the mountain I would find an ancient monster or find some treasure— Yazer Solorzano
- I thought that "tomorrow" was one of the days of the week— Frank