Adding an “-s” to a singular noun forms the plural, but the singular verb has an “-s.” Nouns also have irregular forms that do not follow the “-s” convention. [EDIT]
• Many unusual forms exist for singular and plural nouns. Writers should take care to check on irregular forms. One example concerns “data”:
“Data” is a plural word, thus: Neither NAEP nor PACT provides educators with any valuable data that enhance our ability to teach.
Since many issues with forming the plural for nouns exist (including differences between the U.S. and the U.K about collective nouns), consult a reference when in doubt. One on-line source is the following: