Key to Series

The Key to series is the plain, consumable, single-topic math workbook that has quietly filled the gaps in other programs for four decades. 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
Established	Key Curriculum Press founded 1971; series began in the 1970s; acquired by McGraw Hill in 2012
Website	mheducation.com. Key to series

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 run $3-5 each at current McGraw Hill pricing
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

The Key to series originated at Key Curriculum Press, a Berkeley, California publisher founded in 1971 that specialized in mathematics and geometry materials for middle and high school classrooms. The company was best known in mainstream K-12 for Geometer's Sketchpad, Discovering Geometry, and Investigations in Number, Data, and Space, but among homeschool parents its calling card was always the thin, bright-covered Key to workbooks, which looked like nothing and did the job.

Key Curriculum Press was acquired by McGraw Hill Education in 2012, per McGraw Hill's acquisition announcement, and the Key to catalog has been distributed through McGraw Hill ever since. The acquisition preserved the series intact, the same booklets, the same page design, the same structure. McGraw Hill folded the line into its supplemental mathematics offerings and continues to publish Key to Fractions, Key to Decimals, Key to Percents, Key to Measurement, Key to Algebra, and Key to Geometry as the core six strands.

The Key to series is not a homeschool product by origin. It was written for classroom remediation and for alternative-school settings where students arrive with wildly different math backgrounds and need topical mastery in short cycles. Homeschoolers found it and adopted it, and the booklets became one of the most widely used supplements in the homeschool market. Cathy Duffy's long-running directory lists Key to Fractions, Decimals, and Percents among the most common remediation recommendations in her math section.

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. Within each booklet, every page presents a single concept: a worked example at the top, a short explanation in plain language, and twenty to forty practice problems below. 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. Families using Key to Algebra as a spine typically supplement with a review text before Algebra 2.

A day in the life

A fifth-grader using Key to Decimals as the primary math fits a session into twenty to thirty-five minutes. The student opens the booklet at the marked page, reads the worked example, and completes the ten to thirty problems on that page. A parent checks answers at the end using the answer key. If a concept is missed, the parent re-reads the worked example with the student and assigns the next page. Most days, no presentation is required, the booklet does the teaching.

A ninth-grader remediating with Key to Fractions (because a diagnostic revealed gaps) runs through two to three pages a session, moving faster because the content is below grade level. The same student might use Key to Algebra alongside a full Algebra 1 course as additional practice on a specific weak topic, polynomials, say, picking up only the booklets that cover that unit. The series was designed for exactly this modular use.

What they do exceptionally well

Remediation without shame. Because the booklets are slim, cheap, and explicitly topical, assigning Key to Fractions to a twelve-year-old who missed fractions in fourth grade does not announce "you are behind" the way a repeat of a fourth-grade textbook would. Families routinely use Key to for middle and high school students filling elementary gaps, and the format's neutrality matters. Cathy Duffy's note that the series "can be used for remediation at almost any level" tracks with thirty years of homeschool practice.

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. A family can buy a used copy for under $3 at a homeschool swap and get the same product McGraw Hill sells new. 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. Families whose primary math is faith-integrated often use Key to as a supplement precisely because it adds practice without adding additional worldview content.

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 April 2026, individual Key to booklets retail between $3.50 and $5.00 per unit on the McGraw Hill Key to program page, with answer keys at roughly $6-8 per strand and reproducible test packets at $10-12. A full Key to Fractions set (four booklets plus answer key) runs approximately $20-25. A full Key to Algebra set (ten booklets plus answer key) runs approximately $50-60. These prices have shifted little over the past decade and remain among the cheapest math materials in the homeschool market.

Compared to Saxon Math (a single textbook runs $80-150 with teacher editions and tests adding another $100-150) or to Math-U-See (a single level runs $150-200 for the manipulative-plus-DVD package), Key to is a fraction of the cost and a fraction of the coverage. The right comparison is not to full curricula but to other topical workbooks: Critical Thinking Co.'s math booklets, Spectrum Math workbooks, Kumon worksheets. Against those, Key to is the slimmest and cheapest per unit while being more sequenced.

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 with established school-district distribution, 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 Key to program page, the individual strand pages for Fractions, Decimals, Percents, Measurement, Algebra, and Geometry, and the McGraw Hill acquisition announcement from 2012. We cross-referenced Cathy Duffy Reviews' entry on the Fractions, Decimals, and Percents strands and the publisher's pricing data on each booklet. Prices and program details verified April 2026.