Also the Grade Plan's Grade Descriptions need to be exactly the same. If in one grade plan, one of the words has an "s" and in another grade plan the same word does not have an "s", then the system will display the Grade Description on a new line. 
Note: Also check for extra spaces in the Assessment Grade plan by editing each Row, this is another reason why they may not display correctly even if Sort Order, and Spelling is exactly the same. The Spaces will not display when viewing the Grade Plan, you must edit the Description to see the Spaces.
In order for Grade Descriptions to appear on the same row, they need to be for the same class. For example if the school is using the same grade plan for Kindergarten Homeroom and Kindergarten Language Arts and the school records Tri 1 grades in Kindergarten Homeroom and Tri 2 grades in Kindergarten Language Arts then the grade descriptions will appear to repeat.