We have been using comic life for a while at school and my students really love turning their narratives and information reports into comics or as they are referred to today "Graphic Novels". Comic life will set you back around thirty dollars however and it does have it's limitations.
Comic Master is essentially comic life for free in the browser with nearly all of the features that comic life offers. including the ability to upload your own images set up the style and layout of your comic and obviously add in backgrounds and characters.
All your students will have to do is come up with the plot and go from there. You can publish and print your comic but you will have to go through a free sign up process to actually save it.
All in all Comic Maker is a sure fire winner for students aged from around 10 up and they wil really enjoy turning their texts into an edgy 'Graphic Novel' especially your reluctant writers and readers.
Comic Maker can be found here.