The supposed teacher never wrote it.... it was written by someone else.

http://urbanlegends.about.com/od/barackobama/a/letter_to_obama.htm

Analysis: Readers will either agree or disagree with the opinions expressed above depending on their own political convictions, but the matter of its authorship is subject to correction.

I contacted Kathleen Lyday at Grandview Elementary School in Hillsboro, Missouri, and she told me she did not, in fact, write the letter. More often than not, the signature lines of people who forward such emails are automatically attached in the process and become a semi-permanent feature. This is apparently what happened to Ms. Lyday.

Other variants attribute authorship to "Franklin Bell" or "Douglas M. Casamer." Franklin Bell of Columbia, Maryland is the likelier candidate, given that a version dated April 9, 2009 was posted by blogger Gary Shumway under a preface stating that he had obtained Mr. Bell's permission to do so. (Last updated: 05/27/09)