"He is a student but they are not students."
Translation:Is dalta é ach ní daltaí iad.
I don't understand where the verb "to be" is in the second half of the answer. I thought that "ní" by itself pretty much translated as "not" and therefore needed to be paired with a separate verb, while "níl" was a contraction of "ní bhfuil" so it has the accompanying verb included. What am I missing here?
scríobh mé seo don cheann seo...Is mac léinn é ach ní mic léinn iad agus deir siad go bhfuil sé mícheart...chuir mé tuairisc isteach air.....
It's not correct.
You may have encountered exercises like Dochtúirí atá iontu - "They are doctors" (https://forum.duolingo.com/comment/22847653) or Níl iontu ach dlíodóirí - "They are only lawyers" (https://forum.duolingo.com/comment/9670191). Neither of these constructions will lead to ní daltaí iontu.