>>I now tried the original suggestion.
>
>Did your original suggestion work?

For me it is a little backward, but that works:

IF NOT EXISTS(SELECT column_name  
                     FROM INFORMATION_SCHEMA.COLUMNS
              WHERE TABLE_NAME = N'Volunteers' and COLUMN_NAME = N'IsActive')
   BEGIN
        alter table Volunteers add IsActive bit NULL CONSTRAINT [DF_Volunteers_IsActive] DEFAULT (1)
        EXEC sp_executesql N'UPDATE Volunteers SET IsActive = 1'
   END
 SELECT * FROM Volunteers