I just graduated from the education program at my university and did my student teaching.
For taking notes/writing papers I used Pages.
To make Powerpoints and Presentations I used Keynote.
Remember, with these you can start them on your Mac and seamlessly update them from your iPad and iPhone (iCloud), as well.
For textbooks I used Adobe Reader or iBooks, depending on the type of document. (Some secure PDFs will only open in the official Adobe App)
At the school district where I did my student teaching we used Google Drive to create documents and to share them with students (or have them turn-in to us). The Google Drive App and Quickoffice Apps are really just crap, to put it bluntly, so this was difficult. The best way to manage them is on a regular desktop/laptop. Which was unfortunate, as I would've liked to be able to do more work from my phone/iPad.
For any random time that I felt I needed to hand-write something, or draw a diagram, I used Penultimate (made by the same people as Evernote).
Fortunately for me, iPad came out my Freshman year, so I have been fortunate to have one during the duration of my studies.