Typo check, take it further
It is demotivating to lose an exercise due to a silly typo. Be it an actual typo (such as writing wide instead of wife) or forgetting something like an -s for a plural form.
So why not take the typo check further. If the user gets it wrong by a single letter, display a message like:
"Oops, are you sure you want to check your answer? Check again for mistakes" and then when the user clicks "check" one more time it gives the final answer.
A good idea. Someone else has commented that Duolingo doesn't penalize you for mistyping a single letter but in fact it certainly does if your typo has produced another word. So, in the example of 'wife' and 'wide', Duolingo has no way of knowing that it's a typo, whereas if you had typed 'wief' it would probably pick it up as one. I agree it is frustrating to lose points over something you know is a typo. But I'm not sure there is really a way around this. Perhaps a 'check your answer' for every incorrect answer? I don't know. For me, the issue really only arises in the timed rounds; in the 'normal' lessons, I have time to check my answer before hitting 'enter'. But this brings us back to the old debate about timed rounds. I'm for making the timing optional, as it is in the 30 second timed rounds.