My daughter is 12 now, and reading tons more than when she was 9. The difference is now she has twice daily access to the high school library versus once a week access to an elementary library.

Not sure how much it generalizes, but what would have had her reading more then would have been a well stocked manga section in the elementary library and daily access.

Manga really is an accessible way to get used to reading, and a gateway. She just finished Lord of the Rings.