Go to School Directory
If you are unsure about the person's full name, the School Directory is a good place to begin.
Locate the Parent or Teacher using Grade-level Filters
On the School Directory page, you can see all the parents and teachers who have opted to have their profiles visible in the directory. Parents may choose to display their pictures and their children's first names in their profiles. You can filter the directory by grade.
Go to their Profile and click Message
The profile detail shows Message link next to the parent/teacher profile. Note that a user can opt out from receiving messages. In that case, the Message button does not show up.
Clicking the Message button configures your messaging interface's "To" field, and you can type in your message right away.