When you finish your project and are ready to put the results together, have a look at the 'Communicating Your Results' section of this page:http://www.sciencebuddies.org/science-f ... ndex.shtml
You're correct that the written report usually contains more detail than the poster board. They cover the same information, but people who are standing in front of your board won't have the patience to read the paragraphs of text that you write in your report. Instead, you can summarize the information in bullet points and explain the details while you're talking to them. You might also include more photos, diagrams, and other images on the poster.