These are some sites that might help you with the story Dear Mr. Henshaw.
-http://www.stmschoolpa.com/images/sce/Webquests/third%20grade%20web%20quest
/Dear%20Mr.%20Henshaw%20activities.html
-http://ethemes.missouri.edu/themes/1714
-http://www.scholastic.com/teachers/lesson-plan/dear-mr-henshaw-teaching-plan
