Cover of Mrs. Frisby and the Rats of NIMH

Mrs. Frisby and the Rats of NIMH

by Robert C. O'Brien

Among the most widely assigned — 5 curriculum lists · 7 states

On reading-award lists:Newbery MedalPacific Northwest Young Reader's Choice AwardWilliam Allen White Children's Book AwardMark Twain Readers Award

Mrs. Frisby and the Rats of NIMH by Robert C. O'Brien is assigned in US schools at grades 4–6, with a Lexile measure of 790L. It appears across 5 curriculum references and 7 states, sourced from state DOE pages and AP/IB/Common Core syllabi. Every citation below links to the primary source.

This page shows where Mrs. Frisby and the Rats of NIMH is assigned in US schools — curricula, states, grades, and the primary-source citations behind each placement. Not a summary or study guide.

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Lexile
790L
Grade range
Grades 4–6
Difficulty for grade
Within the grade 4–5 band (740–1010L)
Age range
Ages 9–12
Pages
233
Reading time
about 4h 15m (est.)
First published
1971
Genre
Middle Grade Fiction
ISBN-13
9780689710681

Reading difficulty: At 790L, Mrs. Frisby and the Rats of NIMH falls within the typical 740–1010L text-complexity range for 4th grade (Common Core Appendix A) — a grade-appropriate reading challenge.

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About this book

A widowed field mouse must move her family before the farmer plows over her home, and turns for help to a colony of intelligent rats who escaped a laboratory. O'Brien's Newbery Medal novel is a 4th-6th grade staple with strong thematic depth.

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Why widely assigned

This Middle Grade Fiction title, reads at middle-grade prose complexity, typically at grades 4–6. Written in the 1970s; pairs with curriculum units on family and courage; cited across 5 curriculum frameworks.

Themes

family · courage · science and ethics · intelligence · legacy

Content notes

animal testing · peril

Common Sense Media recommends age 9+.

Where this book is assigned

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Common questions

What grade level is Mrs. Frisby and the Rats of NIMH?
Mrs. Frisby and the Rats of NIMH is most commonly assigned in US schools in grades 4–6, with a Lexile measure of 790L. Specific grade placement varies by curriculum — AP Literature and IB English Literature typically use it in grades 11-12.
What is the Lexile level of Mrs. Frisby and the Rats of NIMH?
Mrs. Frisby and the Rats of NIMH has a Lexile measure of 790L according to MetaMetrics. Lexile measures text complexity, not content maturity — check the grade range and content notes separately for age-appropriateness.
How long does it take to read Mrs. Frisby and the Rats of NIMH?
It takes about 4h 15m to read Mrs. Frisby and the Rats of NIMH (233 pages) at an average adult reading pace of about 250 words per minute — roughly 255 minutes. Faster or slower readers will vary; the estimate is a planning guide for assigning the book.
Is Mrs. Frisby and the Rats of NIMH hard to read for 4th grade?
At 790L, Mrs. Frisby and the Rats of NIMH falls within the typical 740–1010L text-complexity range for 4th grade (Common Core Appendix A) — a grade-appropriate reading challenge. Lexile measures text complexity, not thematic maturity — check the content notes for age-appropriateness separately.
What curricula assign Mrs. Frisby and the Rats of NIMH?
Mrs. Frisby and the Rats of NIMH appears on reading lists for Common Core State Standards (ELA), Mark Twain Readers Award, Newbery Medal, and 2 others. Each assignment on this site links to its primary-source citation.

Why this book is on this list

How we classify

Each dimension below is sourced from a public reference. The full framework is documented on the classification standard page.

Lexile measure
790L — sourced from MetaMetrics’ Lexile Hub.
Grade band
Grades 4–6 — drawn from state ELA frameworks and AP/IB syllabi citing this book.
Curriculum alignment
Cited in 5 curricula on this site (see “Where assigned” above for primary-source links).
State-level evidence
Cited in 7 states ELA frameworks or DOE list (see citations above).
Removal / banning records
No tracked removal or challenge records in cited sources.
Seasonal / contextual tags
Tagged for: award-winner, book-club.

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