Answer:
In a manual for an elementary school classroom.
Explanation:
This answer seems to make the most sense because he wants to include lots of details and <em>very simple words</em> when explaining how to brush teeth. Additionally, dentists, high school students, and the general public who can read essays typically do not need instruction on how to brush their teeth; they should know how to do it already.
My sister-in-law went to Charlie's school
Had to think on this for a bit so hope it is right