World knowledge
Knowledge about the natural and social world is a big, broad unconstrained skill. It is critical for the development of other unconstrained skills, too.
Note: Unconstrained Kids unpacks, translates, and integrates academic research and data about skill type and the science of skill building to support the improvement of PK-12 reading, writing, and mathematics. Despite important differences, all reading, writing, and math skills can be boiled down to two types–constrained and unconstrained. This post is part of a series that provides an overview of both types of skills. This specific post focuses on general knowledge. Like everything on this Substack, this post is a work-in-progress. I will make updates as needed. Footnotes and citations are included at the end. Questions, comments, and suggestions are welcome.
First posted: March 7, 2025
Last updated: April 21, 2026
Three big ideas
Knowledge is the ability to use facts, principles, and ideas to decide and do complex tasks. There are many types of knowledge.
Knowledge about the natural and social world shapes children’s abilities in reading, writing, and mathematics.
Meaningful gaps in knowledge across socioeconomic groups are already present by early elementary school. These differences are shaped by experiences inside and outside of the classroom.
About the data in this post
In this post, I use data from the Early Childhood Longitudinal Study, Kindergarten Class of 1998-99 (ECLS-K). The ECLS-K tracked roughly 22,000 U.S. children from kindergarten (fall 1998) through grade 8 (spring 2007). It’s the best dataset I’ve found to dig deep into individual K-8 reading and math skills. It’s also unique in that it directly assessed children’s general knowledge in kindergarten and first grade. I’ve organized the data by household socioeconomic status. The data are organized by household socioeconomic status.1
What is knowledge?
Knowledge is the ability to use facts, ideas, and principles to decide and do complex tasks (Cantor et al., 2021). This definition comes from what’s known as the “science of learning and development.” This definition has three parts. First, there are things to learn: facts, ideas, principles. Second, there are things to do: decide and do complex tasks. Third, there is capacity: the ability to use what we learn to make decisions and take action. Knowledge is active and dynamic.
This definition parallels that of skill: the capacity to think and act in an organized way in a specific context (Immordino-Yang & Fischer, 2010). Sometimes knowledge itself is referred to as a skill in the context of reading or mathematics (Kim, 2023; Rittle-Johnson et al., 2001). Indeed, the ability to access and use facts, principles, and ideas to engage in goal-oriented behavior is an important part of skill development. Children’s knowledge about the world around them is an essential part of skill building.
There are many types of knowledge.2 The rules of baseball and the strategies of the game. How dinosaurs lived and died. Multi-layered subjects like biology or history. The facts, procedures, and concepts embodied in mathematics. How things work, like the parts of a book or what happens when you go to a restaurant. How different elements of the world — people, objects, ideas — relate to each other, and why. The meanings of words and how they connect to other words, ideas, and principles.
“The knowledge of a word not only implies a definition, but also implies how that word fits into the world” (Stahl, 2005).
Knowledge is a “caught and taught” skill, developing from both informal and formal learning experiences. Unlike constrained skills, any assessment of knowledge will only give us a partial glimpse of a child’s ability to use facts, principles, and ideas to decide and do complex tasks.
Knowledge, reading, writing, and mathematics
In a 2003 article, E.D. Hirsch offers this sentence as an example of the role of general knowledge to reading comprehension:
“Gigantic and luminous, the earliest star formed like a pearl inside shells of swirling gas.”
To comprehend this sentence, Hirsch notes that you rely upon prior knowledge about multiple concepts at once: the Big Bang, pearl formation, the use of metaphor in language, and gasses (Hirsch, 2003). A child who learns to read the words in this sentence will be limited in their understanding if they don’t also understand what the words mean and the embedded concepts and ideas. In other words, they need to understand the world around them.
Although there are many types of knowledge, in this post I focus on what’s alternatively referred to as world knowledge, general knowledge, or background knowledge. These are facts and concepts about the natural and social world. Although there is a distinction between knowledge building and knowledge activation, to keep things simple I refer to both simply as knowledge.
General knowledge represents children’s breadth and depth of understanding of their social and physical environment (i.e., the social, physical and natural world) and their ability to draw inferences and comprehend implications (West et al., 2000). Knowledge about the natural and social world is critical for reading comprehension (Hirsch, 2003; Pearson, et al., 2020; Kim & Cao, 2025), written composition (Graham & Aitken, 2025; Kim, 2025), and mathematical thinking (Grissmer et al., 2010).
General knowledge is an unconstrained skill
The ECLS-K study includes an assessment of K-1 children’s general knowledge of basic natural science and social studies concepts.3 Children were assessed first with a battery of 12 questions, which then determined which of two subsequent versions of the assessment (higher-level or lower-level) they received at the second stage.4
This first chart shows the average number of questions answered correctly by kids on the first-stage assessment. Kids are organized by household income status (quintiles). The dots represent assessments at three points in time: fall kindergarten, spring kindergarten, and spring first grade. Clear gaps existed across social groups in children’s general knowledge, which did not narrow by the end of their second full year in elementary school. (Mouse over the chart.)
To put these data in perspective, this next chart shows the growth pattern for a constrained math skill (relative size) for this same group of kids over the same time period. Early gaps in fall kindergarten are largely closed by the end of first grade. Kids across all socioeconomic groups on average are at or close to full proficiency.
We see similar gap closing for a constrained reading skill (letter-sound correspondence) for the same kids over the same time period.
The knowledge gap is an opportunity gap
The researchers behind the ECLS-K noted the differences in these growth patterns, suggesting that growth in knowledge was also influenced by experiences outside of school in addition to learning in the classroom (Rock & Pollack, 2002). A key difference between constrained and unconstrained skills is opportunity. After all, a constrained skill involves a relatively limited amount of information. All kids who attend school get access to the same information. Mastery is clearly defined and the same for everyone. But unconstrained skills depend more upon opportunities to develop these slower-growing skills inside and outside of school.
For example, children in different socioeconomic groups have different experiences outside of school. This next chart hows participation levels in extracurricular activities for the kids in top and bottom socioeconomic groups in the ECLS-K study during their kindergarten year. These children have vastly different experiences outside of school.
Later surveys in this study also show that children in lower socioeconomic households visit zoos, aquariums, museums, and libraries at significantly lower levels. These differences in opportunity are made more plain by examining differences in general knowledge across socioeconomic levels within a single racial group.5 This next chart shows correct responses to the first-stage general knowledge questions by Black students across five socioeconomic groups. Once again, we see the same stair-step pattern across SES groups and even a further widening by the end of the second year of school.
There is greater use today of knowledge-building curricula in schools compared to 25 years ago. It’s unclear if a similar study today would yield the same results as we see in these late 1990s data. The key point is that knowledge is caught and taught. Kids’ experiences inside and outside of school contribute to the growth of their world knowledge. It plays a complex and vital role in building constrained and unconstrained reading and math skills. Knowledge is the ultimate unconstrained skill.
But wait, there’s more
If you’d like to see more data about constrained and unconstrained skills, check out these other posts on Unconstrained Kids:
Works Cited
Cantor, P., Osher, D., Berg, J., Steyer, L., & Rose, T. (2021). Malleability, plasticity, and individuality: How children learn and develop in context. In P. Cantor & D. Osher (Eds.), The science of learning and development: Enhancing the lives of all young people (pp. 3-54). New York: Routledge.
Fischer, K.W. & Immordino-Yang, M.H. (2002). Cognitive development and education: From dynamic general structure to specific learning and teaching. In E. Lagemann (Ed.), Traditions of scholarship in education. Chicago: Spencer Foundation.
Graham, S., & Aitken, A. (2025). The Writer(s)-within-Community Model. In C. A. MacArthur, S. Graham, & J. Fitzgerald (Eds.), Handbook of writing research (Third). The Guilford Press.
Hattan, C., & Lupo, S. M. (2020). Rethinking the role of knowledge in the literacy classroom. Reading Research Quarterly, 55, S283-S298.
Hirsch, E. D. (2003). Reading comprehension requires knowledge of words and the world. American Educator, 27(1), 10-13.
Kim, Y. S. G. (2023). Simplicity meets complexity: Expanding the simple view of reading with the direct and indirect effects model of reading. In Cabell, S. Q., Neuman, S. B. & Patton Terry, N. (Eds.), Handbook on the Science of Early Literacy, New York: The Guilford Press, pp. 9-22.
Kim, Y.-S. G. (2025). The Science of Reading-Writing Connections. In C. A. MacArthur, S. Graham, & J. Fitzgerald (Eds.), Handbook of writing research (Third). The Guilford Press.
Kim, Y.-S. G., & Cao, Y. (2025). Content knowledge and comprehension: A meta-analytic review of correlational and causal associations. Psychological Bulletin, 151(10), 1219.
Pearson, P. D., Palincsar, A. S., Biancarosa, G., & Berman, A. I. (Eds.). (2020). Reaping the Rewards of the Reading for Understanding Initiative. Washington, DC: National Academy of Education.
Rittle-Johnson, B., Siegler, R. S., & Alibali, M. W. (2001). Developing conceptual understanding and procedural skill in mathematics: An iterative process. Journal of Educational Psychology, 93(2), 346-362.
Rock, D.A. & Pollack, J.M. (2002). Early childhood longitudinal study-kindergarten class of 1998–99 (ECLS–K), psychometric report for kindergarten through first grade (NCES 2002–05). National Center for Education Statistics, Institute of Education Sciences, U.S. Department of Education. Washington, DC.
Stahl, S. A. (2005). Four problems with teaching word meanings. In E. H. Hiebert & M. L. Kamil (Eds.), Teaching and learning vocabulary: Bringing research to practice, (pp. 95-116). Mahwah, NJ: Lawrence Erlbaum Associates, Inc.
West, J., Denton, K., & Reaney, L. M. (2000). The kindergarten year: Findings from the early childhood longitudinal study, kindergarten class of 1998-99. NCES 2001-023. National Center for Education Statistics.
In the ECLS-K dataset, socioeconomic status is defined using a combination of household income, parental education level, and parental occupation.
Hattan and Lupo (2020) describe multiple types of knowledge that children bring to bear for reading comprehension (and presumably also writing and mathematical thinking): cultural, linguistic, principled, strategic, multimodal, multiple text use, and conditional.
Unlike reading and math skills, it isn’t possible to assign proficiency levels to children’s general knowledge (Rock & Pollack, 2002). ECLS-K researchers instead constructed a scale score based upon a two-stage assessment process. Children received a first-stage assessment that consisted of 12 questions. If they got 7 or more questions correct, they were routed to the higher-level assessment at the second stage. Otherwise, they received the lower-level form.
The K-1 general knowledge test was evaluated and found to be free from bias by socioeconomic status (Rock & Pollack, 2002).
The K-1 general knowledge test was evaluated and found to be free from bias against Black students compared to White students (Rock & Pollack, 2002).