Plantzilla by Jerdine Nolen illustrated by David Catrow

Mortimer Henryson takes home a class plant for the summer and writes to his teacher, updating him on the plant's progress.  At first the parents are skeptical of the plant and its unique abilities but in the end are very fond of the plant.
Told via letters between teacher and student.
My sons and I thought the story was a bit weird!
-Borrowed from the library.