You're praising effective practicing habits. You can praise learning from mistakes. That's great.

I always took "A for effort" to be extremely patronizing because I was trying to do the thing right.

The problem is the "A", not the "A for effort". "A for results" just highlights an arbitrary bar that is likely too low or too high.

I guess a modification on that accounting for the expected performance would make sense.

It might be praiseworthy, but I was talking from the perspective of using praise to improve attainment. Dweck has written about the misapplication of her theories in recent years: http://www.edweek.org/ew/articles/2015/09/23/carol-dweck-rev...