Thanks. I missed the variable assignment.

>You didn't assign any value to output parameter in the dynamic SQL. Try

set @sql = N'select @id = in_lname from ' + @table + ' where in_id = 7'
>

N'@id nvarchar(50) output' defines parameters passed into sp_executesql. @id output is actual parameter passed. They don't have to have the same name. See BOL for details.
>
>>I don't seem to make it work. See below. What is the purpose of the output param being listed twice?
>>
>>Thanks
>>
>>

>>declare @id nvarchar(50), @sql nvarchar(500), @table varchar (50)
>>set @table = 'intake'
>>set @sql = N'select in_lname from ' + @table + ' where in_id = 7'
>>
>>exec sp_executesql @sql, N'@id nvarchar(50) output', @id output
>>
>>if @id is null
>>  print 'null'
>>else
>>  print @id
>>

>>
>>Prints null every time.
>>