Bullfrog Books; Cat Club Books in Order

Series books grow with readers — but that's also the trap. Most series start at one reading level and one content intensity and drift upward over the course of the run. Bullfrog Books; Cat Club (2 books by Cameron L. Woodson) lands at a grade 1 reading level, with average content intensity 1/5. Intensity stays consistent across the series, so a reader who can handle the first book can generally handle the rest.

The reading-order table above lists every book with per-volume reading level, age and intensity ratings so you can spot any escalation before it catches your reader off guard. For a deeper dive into how we score text difficulty vs. emotional weight separately — and why series readers especially benefit from that split — see our methodology page.