What is your budget? Size wise the iPad mini is larger and you can do a little more with it, but the iPod touch is more compact and better suited for other things. What would you use either of these for? Games? Reading? Music? The iPad Mini will have a battery life than the iPod Touch..
This right here makes the iPod Touch utterly useless. I have a 7" tablet and an iPod Touch and I can safely say that the Touch would never get used for homework over the Nexus 7.I'd use it for homework docs