21st Century Junior Library: Which is Which? Books in Order
8 books by Tamra Orr. Reading level: Grades 3.6–3.9. Lower Grades (Ages 5–8).
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 reading level Grades 3.6–3.9, with average content intensity 1/5. Intensity stays consistent across the series — a kid who can handle the first book can generally handle the rest.
The reading-order table below lists every book with per-volume reading level and intensity badges 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.
Content Intensity Across the Series
ConsistentContent stays at a steady intensity level throughout the series.
21st Century Junior Library: Which is Which? Reading Order
| # | Title | Reading Level | Content |
|---|---|---|---|
| 1 | Aardvark or Anteater Tamra Orr | Level 3-4 | Gentle |
| 2 | Alpaca or Llama Tamra Orr | Level 3-4 | Gentle |
| 3 | Butterfly or Moth Tamra Orr | Level 3-4 | Gentle |
| 4 | Crocodile or Alligator Tamra Orr | Level 3-4 | Gentle |
| 5 | Frog or Toad Tamra Orr | Level 3-4 | Gentle |
| 6 | Porpoise or Dolphin Tamra Orr | Level 3-4 | Gentle |
| 7 | Seal or Sea Lion Tamra Orr | Level 3-4 | Gentle |
| 8 | Wasp or Bee Tamra Orr | Level 3-4 | Gentle |
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
Questions about the 21st Century Junior Library: Which is Which? series
- What reading level is the 21st Century Junior Library: Which is Which? series?
- The 21st Century Junior Library: Which is Which? series by Tamra Orr is at a Grades 3.6–3.9 reading level (average Grade 3.8). Intended for Lower Grades (Ages 5–8). There are 8 books in the series.
- What order should I read the 21st Century Junior Library: Which is Which? books?
- The reading-order table above lists all 8 books with per-volume reading level and intensity ratings. Start with book 1 and read in publication order unless the table indicates a different recommended order for newer readers.
- What age is the 21st Century Junior Library: Which is Which? series appropriate for?
- The 21st Century Junior Library: Which is Which? series is recommended for Lower Grades (Ages 5–8). The average content intensity is 1/5. Check the intensity trajectory above to see whether content gets heavier across the series — if it does, sensitive readers may want to stop earlier in the run.