Key to Series

The Key to series is a plain, consumable, single-topic math workbook series. It is not a full curriculum, and it is not trying to be.

Last updated: 2026-04-24 · Every Homeschool Editorial Team

At a glance

Method	Subject specialist / topical workbook / mastery-oriented
Worldview	Secular
Grades	Roughly grades 4-12, depending on strand
Formats	Consumable print workbooks; companion answer keys
Cost tier	Budget
Parent intensity	2
ESA-common	Yes, on most workbook-eligible marketplaces
Accredited	No
Website	mheducation.com. Key to Fractions, Books 1-4 set

Our scoreboard (1-5)

Criterion	Score	One-line reason
Academic rigor	3	Solid arithmetic and pre-algebra coverage within each strand; does not replace a full curriculum
Ease of teaching	5	Minimal parent presentation; student reads the worked example and does the page
Content quality	4	Tight, sequenced, and honestly paced; free of pedagogical fads
Flexibility	5	Each booklet stands alone; used for remediation, supplement, or primary, per parent choice
Value for money	5	Booklets list at $8.84 each and four-booklet sets at $33.24 on McGraw Hill's site as of October 2026
Worldview scope	5	Fully neutral; no narrative, no illustrations beyond geometric figures
Visual/design	2	Black-and-white, no-frills layout unchanged since the 1980s
Support resources	2	Answer keys and reproducible tests exist; no videos, no teacher training, no community

Who the publisher is

McGraw Hill publishes Key to Fractions, Key to Decimals, Key to Percents, Key to Measurement, Key to Algebra, and Key to Geometry as the core six strands.

Cathy Duffy's review of the Key to series describes the Fractions and Decimals strands as not complete math courses but fairly complete courses on their topics for children about age nine and older, and describes Key to Fractions as particularly useful for students who need extra help with that topic.

The core pedagogy

The series is topical mastery, taught by the page. Each strand covers one mathematical area in depth across four to ten consumable booklets. Key to Fractions, for instance, runs four booklets. Key to Algebra runs ten. Per Cathy Duffy's review, the booklets have lots of white space and few problems per page, and they emphasize concepts with pictures and easy-to-understand explanations rather than drill work. The student reads, works the page, and moves on. The parent's role is to check answers against the companion answer key.

The pedagogical logic is incremental mastery without spiral. Unlike Saxon or Abeka, Key to does not return to fractions every year for deepening; it treats fractions as a topic to be finished and moved past. A student who completes all four Key to Fractions booklets has been walked through every operation (addition, subtraction, multiplication, division, mixed numbers, equivalent fractions, simplification) in a linear sequence and has done several hundred practice problems along the way. The same is true for each other strand.

Signature mechanics: (1) Single-topic booklets, the Fractions strand does not teach decimals; the Decimals strand assumes fractions are done. Topics stay in their lanes. (2) Worked example format, every concept is introduced by solving a sample problem, not by narrative explanation. (3) Scaffolded practice, within a page, problems progress from guided (fill in one blank) to independent (solve from scratch). (4) No illustrations beyond mathematical figures, the books contain diagrams where geometrically useful and are otherwise uncluttered by stock art or narrative.

High school strands (Algebra, Geometry) cover less ground than a full textbook. Key to Algebra's ten booklets take a student through linear equations, graphing, polynomials, factoring, quadratics, and a first pass at systems; they do not cover the full Algebra 1 sequence that, say, Saxon Algebra 1 or Art of Problem Solving would.

What they do exceptionally well

Remediation without shame. Because the booklets are slim, cheap, and explicitly topical, assigning Key to Fractions to an older student who missed fractions earlier does not announce "you are behind" the way a repeat of an elementary textbook would. Cathy Duffy's review notes that Key to Fractions is particularly useful for students who need extra help with that topic (Duffy review).

Durable simplicity. The series looks the same today as it did in 1990. There are no apps, no subscriptions, no online components, no login requirements, no updates that break the prior edition. This durability matters for multi-child families and for long-horizon planning.

Neutrality across worldviews. Because the series is secular and contains no narrative, no illustrations of people, and no cultural references, it slides into any curriculum mix. Abeka, Memoria Press, Oak Meadow, secular eclectic, without friction.

What they do poorly

Not a full curriculum. The six strands together do not constitute a complete K-12 math sequence. A family using only Key to would miss elementary arithmetic scaffolding (the series assumes whole-number operations before Fractions), would lack conceptual depth in geometry (Key to Geometry is proof-light compared to a traditional high school geometry text), and would have no statistics, probability, or pre-calculus coverage. Families who try to use Key to as a primary K-12 spine will stall out.

Visually austere to the point of boredom. For a student who needs color, narrative, and variety to engage, Key to is a hard sell. The black-and-white page layout and the sameness of the format across hundreds of pages produces its own fatigue. Families whose children do best with Beast Academy, Singapore's illustrated textbooks, or Life of Fred's narrative approach will find Key to unappealing even when it would work.

No teacher support infrastructure. McGraw Hill sells the books and the answer keys. There are no instructional videos, no parent training, no homeschool-specific scope-and-sequence guide, and no active community forum. Parents who want to be taught how to teach a concept alongside their child (what Teaching Textbooks or Math-U-See provide) will find Key to silent on pedagogy. The booklet is the instruction.

Who it fits / who it doesn't

• Pick Key to if: you need cheap, topical remediation for a specific math gap; your primary curriculum needs supplemental drill and your child already dislikes the primary text; you want a secular math resource that will not interfere with a faith-integrated main program; your student is self-directed enough to work through a worked example and a practice page without presentation; you are an eclectic homeschooler assembling math from multiple publishers.

• Skip Key to if: you want a complete K-12 math curriculum (use Saxon, Math-U-See, Beast Academy, Singapore, or Art of Problem Solving instead); your child needs visual engagement, narrative, or video to stay with math; you want integrated scope-and-sequence tracking across all strands; you want a teacher-guided program with parent-training support.

Cost honest assessment

As of October 2026, McGraw Hill lists an individual Key to booklet at $8.84 and the multi-booklet sets at $33.24 for Key to Fractions, $33.24 for Key to Decimals, $33.24 for Key to Measurement, $24.36 for Key to Percents, $81.68 for Key to Algebra, and $86.20 for Key to Geometry. Each strand also has a teacher's guide with answers, and an optional Reproducible Tests book is available for some strands, per Cathy Duffy's review; those items are priced separately from the student booklets.

Key to covers one topic per strand rather than a full curriculum, so the right comparison is not to full curricula such as Saxon Math or Math-U-See but to other topical workbooks: Critical Thinking Co.'s math booklets, Spectrum Math workbooks, and Kumon worksheets.

ESA eligibility notes

The Key to series is typically eligible on state ESA marketplaces that permit McGraw Hill supplemental materials; because the books are published by a mainstream secular educational publisher, they clear religious-content restrictions that narrow which products qualify in some states. Eligible marketplaces commonly include Arizona's Empowerment Scholarship Account program, Florida's MyScholarShop platform, and Utah's Utah Fits All Scholarship. Families should verify within their specific state portal that the particular Key to strand is listed before ordering.

Alternatives

• Critical Thinking Co. Mathematical Reasoning, a family would choose this over Key to for a more engaging visual design and a stronger word-problem emphasis at the elementary level.
• Kumon workbooks, a family would choose Kumon over Key to for more concentrated daily drill on a single operation at a time, with cleaner pages and brighter design.
• Life of Fred, a family would choose Life of Fred over Key to for narrative-driven math that builds conceptual understanding through story rather than practice pages.

How we verified this

Our editorial team reviewed the McGraw Hill product pages for the Key to Fractions, Decimals, Percents, Measurement, Algebra, and Geometry sets linked above and Cathy Duffy Reviews' entry on the Key to series. Prices verified October 2026.