Mai Nada is an interesting site for making digital comics. Unlike other sites MN focuses on having users draw their own comic. Once a comic is done it can then have pre-set timings to allow the comic to animate on its own (think Comic Life movie export feature). Keep in mind this site is also an online community so it may not be appropriate for school.
I recommend checking out Mai Nada by clicking here!!
For my top 10 digital comic creators click here.