There are many speakers available to come and talk to your middle- or high-school students about drug and alcohol abuse. Many of these speakers have overcome addiction themselves, and have gripping stories about their own issues that led to addiction that can serve as useful cautions for students. Combining these stories with positive stories involving perseverance, these speakers often talk about how they overcame hitting rock-bottom.
There are some motivational speakers and groups that come to school assemblies and put on exciting exhibitions before talking to students about perseverance and other important traits. They break boards, shred phone books with their hands and get the students buzzing, then turn to more important topics. The students are engaged because of what they've just seen and are more likely to listen to the message. Commandos USA is one of these groups.
Congressional Medal of Honor recipients can make for unforgettable speakers for school assemblies. Having received the highest recognition possible for their heroism, many of them have devoted themselves to patriotic education as a calling. They can talk about the battles in which they earned their medals and move on to the importance of perseverance for students.
Motivational speakers who have had successful careers in the NFL, NBA, NHL or Major League Baseball can make for captivating motivational speakers. Many of even the most fidgety members of your assembly audience will pay rapt attention to someone who made it into the professional ranks of their favorite sport, and the rigors of competing at the highest level can instill wisdom in what it takes for students to persevere.