I find that many students need to practice speaking in front of the classroom a few times in order to get comfortable (somewhat) when giving more lengthy presentations.
As a 4th grade teacher, my students are required to memorize the Preamble to the Constitution and recite it to the class to celebrate Constitution Day in September. I give each student a handout of the Preamble and the accompanying rubric and have them practice for a week. I'm always amazed at how much they practice and how well they perform.
Included are both short and lengthy texts such as quotes, songs, and excerpts from speeches and historical documents.