Gaining the ability to read begins from birth, and by the time that kids are school age they should be clamoring for books if the parents did their job.
After time-worn basic reading instruction in first grade, it's a matter of parents enforcing reading-time at home for school mandated reading. Then providing access to the reading material that the child desires for their free reading. Whatever it is. Book-bound comic strips are an early popular grade-level choice, and are fantastic. If a child is behind, then go simpler. Everything else is a band-aid or less practical if not detrimental in comparison. Some kids need services if they have deficits, but that doesn't imply that the standard practice is flawed. All top readers came out of this type of early progression. So have most middling readers, often just separated by the amount of time they've chosen to put in. Or were compelled to put in.