***** NOT A TEACHER *****
Good afternoon, Ademilson.
(1) Hopefully, one of the teachers will soon tell you and me the answer.
(2) May I just offer these ideas:
(a) Maybe many native speakers think both are "correct."
(b) Most books tell us that the comparative and superlative of adverbs are
used the same as the comparative and superlative of adverbs. That is,
use the comparative when two things are compared; use superlative when
three or more things are compared.
(i) Of course, there are many exceptions to the "rule."
(c) Here is a sentence from Mr. L. G. Alexander's very popular LONGMAN
I work FASTEST when I'm under pressure.
(i) Mr. Alexander used the superlative. Many (maybe!) because of all the
different working conditions that are possible, the condition of my being
under pressure makes me work fastest.
(d) So let's look at your examples:
(i) Some people learn BETTER by going to class.
(a) Maybe (maybe) that means that they learn better by going to class THAN some other way (for example, taking classes on the Internet).
(ii) Some people learn BEST by going to class. Of the many ways to learn (going to class, taking classes on the Internet, hiring a tutor, being an apprentice, taking correspondence courses), going to class is how some people learn best of all.
Have a nice day!