Voted Best Answer
Dec 04, 2018 - 01:13 PM
The 's in English is used to mark the possessive here, not the plural
And the "en" at the end of "Student" in German is here because Student is part of a special group of masculine nouns that we call "weak masculines" in German grammar. All these nouns, like der Student, der Name, der Kollege etc take on a final EN in any case but the Nominative case (subject).
if you want to review them you can go back to the tutorial of German 4 session 9.
If we were referring to several students though, you're right that the phrase would be: Ist das die Nummer der Studenten? /Is that the students'(p/m) number?
Hope this helps!