"I am a pupil."
Translation:Mi estas lernejano.
lernanto is someone who learns, a learner.
lernejano is someone who is a part of a place of learning, i.e. someone who attends a school.
As for Esperanto, that comes from Zamenhof's pseudonym "Doctor Esperanto", where "esperanto" means "one who hopes".
I think the language was, at first, simply called "Lingvo Internacia" (International language) but got called "Esperanto" after that pseudonym as well.
Nowadays, it's best to treat "Estperanto" as simply a word by itself rather than trying to analyse it as esper/ant/o "a hoper".
My understanding: The "ant" root means "present action/actor". So "lernanto" means "one who learns". The "an" root means "member" but you wouldn't just be a member of learning, so the other accepted answer is "lernejano" which combines "ej" (place) with "an" (member) giving "member of a school".
"Learner" seems fine for "lernulo". "Lernejanto" doesn't make much sense as a word. It would be like "learning place do-er" which maybe you could read as "student", but the "ant" participle attaches to verbs, and it is hard to imagine what "learning place" as a verb ("lerneji"?) would mean. Participles are covered in the "Education" lesson if you're not familiar with them yet. Or maybe you meant to write "lernejano" (learning place member) which is completely acceptable as student or pupil.
Just a note; should one of the developers review this comment. The top-most 'hover hint' for "pupil" is in the accusative. Since that follows "estas", then of course it wouldn't be in the accusative.
(I didn't use the 'report' button because we have been cautioned [in the FB group] on using the 'report' button too much until after the course has exited Beta Status.)