I’m sure different students will seek different apps depending on what they’re majoring in to. Google translate is a popular one for general uses in language-oriented class, WPS office allows you to work/fix your work on phone, any photo-editor apps will help if you’re in photography or visual-design class, and I’m sure there are many more depending on what feature you’re looking for.

I must also mention that there are ‘games’ in nds that are made to help people that have taken interests in certain field (and you can utilize this using a nds emulator for your mobile phone), for example if you’re a student majoring in certain language then “My Spanish/Japanese/Mandarin Coach” will definitely help as well as entertain you in learning a specific language. If you’re in to culinary class then “Personal Trainer: Cooking” will be a great addition for your cooking practice.

Depends on the grade level. My Kindergartner granddaughter is having great success with learning to read through some apps like Letter Bingo and Word Bingo.

That would not be appropriate for a 6th grader.

You need to narrow down your question.

There are several apps available from Adobe on Android and iOS. Such as Adobe Illustrator Draw. I’ve tried it on the iPad and if you have a stylus pen it’s a really great app.

There is also the Lynda app (available on all platforms) for IT / graphic design training.

I’ve also discovered that the Dictionary.com app for the iPhone is really cool. It gives you word of the day notifications everyday. Excellent interface too.