It is, in my opinion, just that side of 'too small' to be a 5-days-a-week, 6-hours-a-day tool for pupils. It is in no way too weak a computer to be used that way. I just think that the more restricted keyboard will prove tiring and the fractionally more cramped UI will show itself as problematic over extended use.
Exactly the words I was looking for, but rather failed to find.
This is exactly why I just received notification from Apple on my refund for the iPad Mini. Unlike Fraser, I couldn't get "over it", even after a few attempts:
The second week, though, was different. I was teaching all week and didn't really have time to chew over questions of should-I-use-this-iPad-or-that-iPad, I just had to get my gear and get up in front of classes hour after hour after hour. It got to Friday and I realised that I had literally not touched my 3rd-generation iPad all week.
Roll on the iPad Mini 2 with Retina Display.