I told my children to make up a fictional persona to write about, and that I would back them up completely if they were ever questioned or criticized about it. The poor child who shares honestly, who doesn't realize or isn't capable of putting on a front, will be teased mercilessly (speaking as having been that child). For others, it's license and endorsement for fake honesty.
The link to Jessica Lahey's piece about making her middle school students squirm by writing about something personal appears to have been removed. I doubt that Ms Lahey has changed her mind about the value of the assignment, but probably just got tired of hearing negative comments.
This site uses left-brain and right-brainnot as physiological terms for the actual left and right hemispheres of the brain, but as they are employed in the everyday vernacular. They appear here in the same spirit in which people use type A and type B (themselves the relics of a debunked theory about blood type and character type): an informal shorthand for certain bundles of personality traits.