I think they would wish for some more adornment around the school campus for the special function.

Adornment means something that adds beauty or embellishment, such as decorations or ornaments. Decoration is the direct synonym meaning the act or process of decorating or something used to add beauty. Subsummation refers to the act of subsuming under a category; coloration means the arrangement of colors; inculcation means the act of teaching by repetition. Therefore, decoration is the correct synonym.