They’re becoming better readers.
The word-by-word style of reading your child previously had might be switching over to an easier, smoother technique in third grade. Many children begin to have a passionate love of books at this age.
What you should do: Encourage reading and make use of the local library. If your child can read fluently, challenge her to read above her grade level. If your child is struggling, seek tutoring or testing that can determine why.