Is better to read with mind or with your voice?

it is said that it is better for some people to read in there mind but, that is not completely true in one study it proves that it is easier for kids between the ages of 4-15 to remember what they hear instead of what is in there mind because they are listening which keeps them awake and aware as for in there mind they begin to grow tired and sleepy also some people have different reading speeds and some may fall behind if they don't finish in time and the teacher will never know how good the kids the really read if he/she can not hear them.