You should use more than just that book for referencing, because I've heard it isn't very accurate (but then I've only heard it from teenagers that are absolutely and sickeningly obsessed with Eric and Dylan. Even so you should research around the web, too. http://acolumbinesite.com/ is absolutely great for information about everything relating) in way of the two boys' lives. Also something interesting would be for you to search the 'Columbine' tag on tumblr. You'll be pretty disturbed by some of the people on there... the things they talk about, and how they are, but it might be a good thing if you're interested in the different ways people have reacted and still react to Columbine.
Also, the media really screwed up the coverage of Columbine, and a lot of people don't know any more about it than what they watched on television that day. So your teacher might have only known about it from news articles and/or television.
The Columbine shooting is definitely one of the things that changed my life, besides 9/11 and the sniper shooting in Maryland, especially since my family knew a victim who was murdered by those sick psychos.
Also, the media really screwed up the coverage of Columbine, and a lot of people don't know any more about it than what they watched on television that day. So your teacher might have only known about it from news articles and/or television.