Making mistakes is inevitable in young students during the learning process, but what matters is that those mistakes are picked up on.
It is not enough to point out the mistake but to also understand the reason they were made in the first place.
When a child undergoes a standardized test it is crucial to sit with them and go through their incorrect answers. It is also a good idea to get them to re-work problems that are missed on science and math tests and to get them to rewrite short answer questions and essays based on the feedback they receive from their teachers.
If they are reading, either for school or for pleasure, get them to tell you about the book. Find out if they really understand what they are reading. You might also want to encourage them to look up and find out the meaning of words that they may not have previously been familiar with that they encounter during their read.