Multiple resizable columns with the gridsplitter

I need to make multiple columns resizable using the grid splitter, however, when I resize the column, the content in the column stays the same width.  below is some simple xaml that demonstraights this.  Can someone kindly show me how to make this work?

Thank you.

<Grid x:Name="LayoutRoot" Background="White"><Grid.ColumnDefinitions><ColumnDefinition Width="150"  /><ColumnDefinition Width="10"  /><ColumnDefinition Width="150"  /><ColumnDefinition Width="10"  /><ColumnDefinition Width="150"  /><ColumnDefinition Width="10"  /><ColumnDefinition Width="150"  /><ColumnDefinition Width="*"  /></Grid.ColumnDefinitions><sdk:GridSplitter  Grid.Column="1" Background="LightGray"/><sdk:GridSplitter  Grid.Column="3" Background="LightGray"/><sdk:GridSplitter  Grid.Column="5" Background="LightGray"/><TextBox Grid.Column="0" Background="Azure" /><TextBox Grid.Column="2" Background="Azure"  /><TextBox Grid.Column="4" Background="Azure"  /><TextBox Grid.Column="6" Background="Azure"  /></Grid>