The score board is for the whole class. If all the great suggestions that you have had so far doesn't work for you, you do have the option of going to an independent scoreboard for those who are causing the problems. Have you read the ebook "Teaching Challenging Elementary Students"? Chris has a ton of great suggestions on dealing with those hard to handle kids such as the independent scoreboard, the "Bulls-eye Game", "Practice Cards", and The Agreement Bridge". All of this is a process. He tells you step by step, do this until it doesn't work, then do this. He even has variations to the scoreboard he presented in one of the topics in his web series. There is always more support for you in WBT. Just look through the free downloads.
Best of luck to you. Keep us posted.