Other tests (DIBELS comes to mind) may have a lot more data behind them, but in an opinion formed over 28 years in the classroom and watching students go on from kindergarten into the grades to come, there is simply no other indicator that is as predictive of reading success as knowing all the sounds in the Soundabet.
It always makes my day when someone adds this accomplishment to their kindergarten credentials.
Today was Luke's day. Here he is:
There's a whole posse of students right behind him.