21st Century Junior Library: Which is Which? Books in Order
21st Century Junior Library: Which is Which? is an 8-book series by Tamra Orr for ages 5–8, at a grades 3–4 reading level, with gentle content (HootRated intensity 1/5).
- Books
- 8
- By publication date
- Content intensity
- Gentle
- HootRated 1/5
21st Century Junior Library: Which is Which? Reading Order
Series numbers aren't available for most 21st Century Junior Library: Which is Which? books, so they're listed by publication date (oldest first).
| # | Title | Reading Level | Ages | Content |
|---|---|---|---|---|
| 1 | Aardvark or Anteater 2019 | Level 3-4 | 5-8 | Gentle |
| 2 | Alpaca or Llama 2019 | Level 3-4 | 5-8 | Gentle |
| 3 | Butterfly or Moth 2019 | Level 3-4 | 5-8 | Gentle |
| 4 | Crocodile or Alligator 2019 | Level 3-4 | 5-8 | Gentle |
| 5 | Frog or Toad 2019 | Level 3-4 | 5-8 | Gentle |
| 6 | Porpoise or Dolphin 2019 | Level 3-4 | 5-8 | Gentle |
| 7 | Seal or Sea Lion 2019 | Level 3-4 | 5-8 | Gentle |
| 8 | Wasp or Bee 2019 | Level 3-4 | 5-8 | Gentle |
Content Intensity Across the Series
ConsistentContent stays at a steady intensity level throughout the series.
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. 21st Century Junior Library: Which is Which? (8 books by Tamra Orr) lands at a grades 3–4 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.
All 21st Century Junior Library: Which is Which? Books
Aardvark or Anteater
Tamra Orr
Aardvark or Anteater
Tamra Orr
Alpaca or Llama
Tamra Orr
Alpaca or Llama
Tamra Orr
Butterfly or Moth
Tamra Orr
Butterfly or Moth
Tamra Orr
Crocodile or Alligator
Tamra Orr
Crocodile or Alligator
Tamra Orr
Frog or Toad
Tamra Orr
Frog or Toad
Tamra Orr
Porpoise or Dolphin
Tamra Orr
Porpoise or Dolphin
Tamra Orr
Seal or Sea Lion
Tamra Orr
Seal or Sea Lion
Tamra Orr
Wasp or Bee
Tamra Orr
Wasp or Bee
Tamra Orr
Series Like 21st Century Junior Library: Which is Which?: What to Read Next
Similar reading level, content intensity and themes.
- 21st Century Skills Library; Exploring Our Rainforests by Tamra Orr 5 books · Grades 4–5 · gentle content
- Science Explorer: Follow the Clues by Tamra Orr 5 books · Grades 4–5 · gentle content
- Phonics Readers by Carol K. Lindeen 7 books · Grades 2–4 · gentle content
- Music Makers; Musical Instruments (Child's World) by Pamela K. Harris 6 books · Grades 3–4 · gentle content
- Science Readers: Content and Literacy-Grade 2 by William B. Rice 3 books · Grades 3–4 · gentle content
- Smithsonian Little Explorer; Little Physicist by Megan Cooley Peterson 4 books · Grades 3–4 · gentle content
Questions about the 21st Century Junior Library: Which is Which? series
- What reading level is the 21st Century Junior Library: Which is Which? series?
- 21st Century Junior Library: Which is Which? books are at a grades 3–4 reading level (average grade level 3.8), and HootRated recommends the series for ages 5–8. There are 8 books in the series.
- What order should I read the 21st Century Junior Library: Which is Which? books?
- Series numbers aren't available for most 21st Century Junior Library: Which is Which? books, so HootRated lists them by publication date: Aardvark or Anteater (2019); Alpaca or Llama (2019); Butterfly or Moth (2019); Crocodile or Alligator (2019); Frog or Toad (2019); and 3 more.
- What age is the 21st Century Junior Library: Which is Which? series appropriate for?
- HootRated recommends 21st Century Junior Library: Which is Which? for ages 5–8. Content is gentle (HootRated intensity 1/5). Intensity stays consistent across the series, so a reader who can handle the first book can generally handle the rest.