Of course, you can talk to his teacher about it.
You can also in the meantime just have him read more at home. My second grader this year did a reading contest at school- he read 400 books or book chapters in 4 months. He started reading ALOT at home for this silly contest- magically, his reading skills just jumped.
You could read a book with him and have like a book club at home where you discuss it. Etc.