Ipad Air vs Sony Xperia Z2 (or maybe other tablet?)

how about beeing a "pirate"?

buy a Nexus 7 and be reborn :) The best tablet in price/quality :)

Both of them are great, really depends on whether you want Android/iOS and how important waterproofing is to you.

I own both Xperia phones and iPads, and their build quality are pretty extraordinary. You pay for what you get.

Other tablet?
Surface Pro. (the first one)
We bought one when it was on sale for $499 (they are no longer being made), so it was worth it imo.

The biggest most important questions you need to ask yourself. "Do I really need a tablet?" "What will I do with it and is that really something I need?"

Also if you hate tablets and you'll be mostly taking notes and such, have you thought about a Chrome book? Super light and about $200.

I had the same question and I consider to buy Z2 because of great design, water resistant, lightness. Now it replaces my notebook. I can easily bring it to any place and use it in any occasions and nothing would hamper me. So for me Z2 is a perfect assistant in my everyday life

iPad Air. I have one and it has great design and quality.

make some notes and play games

Neither will be any good for school. Get a light laptop.

I'd choose the Xperia Z2 over the iPad Air anytime.

As other mentioned, if looking only at school work, a Chromebook might fit your needs better. The tablet will be more versatile, but you might want to consider something like this if you will be taking a lot of notes with it.

How heavy is your laptop? It may not be too difficult to find a lighter one. Windows tablets with keyboard can be a good choice, the ASUS T100. I have the ASUS M80TA (VivoTab Note 8), with a case and keyboard it weights 700g. Not totally usable as a laptop (keyboard is cramped), but still pretty good.

approx 3 kg. but i have very heavy books that's why i thought about something lighter

Get a Windows 8 tablet. I own both the Nexus 7 and a Ipad Air. But in the end I just keep using my Lenova Miix 2 8". It's literally a computer but then tablet sized. While the Nexus and Ipad are just tablets with an phone OS on them.