The class was hard, and at first some of the students didn't like the fact that Mrs. Arellano kept us active for the whole fifty minutes every day.
Grammatically can we omit the fact and use that only?
***** A NON-TEACHER's COMMENT *****
(1) I believe that the answer is NO.
(2) I do believe that the following would be fine:
The students didn't like it that Mrs. Arellano kept us active for the
whole fifty minutes.
(a) The sentence would then be:
The students didn't like it.
("That Mrs. Arellano kept us .... " would then be a noun clause in
apposition with "it." That is, explaining "it.")
(3) Two extra points:
(a) I think that you are very smart not to use "the fact that."
Writing teachers always warn us against using unnecessary words.
(b) I think that some native speakers would not have a big problem
if you used only "that":
Hey! I don't like (it) that you are always insulting me.