Show me the data: 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 constrained and unconstrained skills for people that run, fund, and assist organizations that teach and serve kids. This post presents a series of charts I created from among four nationally representative datasets to illustrate proficiency patterns in representative groups of constrained and unconstrained reading and math skills, unconstrained nonacademic skills, and unconstrained general knowledge. For reference, see this working list of constrained and unconstrained skills. Like everything on this Substack, this post is a work-in-progress. I will make updates as needed. A list of the skills included in these charts is included at the end. Questions, comments, and suggestions are welcome.
Last updated: March 15, 2025
Three big ideas
Knowledge is the ability to use facts, principles, and ideas to decide and do complex tasks. Knowledge is sometimes referred to as a “skill” in the context of reading and math (vocabulary knowledge, conceptual knowledge). This is akin to the way that cognitive scientists describe skill building as constructing and generalizing new knowledge to different tasks and contexts.
Early knowledge gaps as children start elementary school appear to be heavily shaped by their experiences outside of school. Twenty-five years ago, these gaps did not appear to narrow in the first years of school. It’s possible this might be changing with the adoption newer knowledge-building curricula.
Knowledge appears to be moderately correlated with overall reading and math achievement. Below the surface, however, is a dynamic relationship between knowledge and constrained and unconstrained reading and math skills.
About these data
The data in these charts come from the Early Childhood Longitudinal Study, Kindergarten Class of 1998-99 (ECLS-K). I've provided an overview of these and other datasets I used to analyze constrained and unconstrained skills. The ECLS-K data were collected between Fall 1998 and Spring 2007. It is unique in that it includes information about children’s knowledge in addition to their reading and math skills. I used the EdSurvey R package to analyze the data. The data are organized by household socioeconomic status. In the ECLS-K dataset, socioeconomic status is defined using a combination of household income, parental education level, and parental occupation.
What is knowledge?
Knowledge is the ability to use facts, principles, and ideas to decide and do complex tasks (Cantor et al., 2021). 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.
Knowledge is critical for reading comprehension (Hirsch, 2003; Pearson, et al., 2020). 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). Content knowledge, background knowledge, text structure knowledge, and morphological knowledge are component reading skills.
Vocabulary, a critical component skill for both reading and math, is also a type of knowledge. “The knowledge of a word not only implies a definition, but also implies how that word fits into the world” (Stahl, 2005). Factual (or declarative) knowledge, procedural knowledge, and conceptual knowledge are the three primary components of mathematics. Hattan and Lupo (2020) remind us there are multiple types of knowledge that children bring to bear for reading comprehension (and presumably also mathematical thinking): cultural, linguistic, principled, strategic, multimodal, multiple text used, and conditional.
Knowledge is a “caught and taught” skill, developing from both informal and formal learning experiences. The breadth and depth of these different aspects of knowledge illustrates its nature as a “large problem space” (Snow & Kim, 2007). 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.
Gaps in general knowledge are hard to close
The ECLS-K study includes an assessment of K-1 children’s general knowledge of basic natural science and social studies concepts. These are topics that were not formally included in typical kindergarten and first grade curricula in the late 1990s. In fact, researchers expected children’s knowledge in these areas to stem from “his or her family background, home educational environment, and preschool experiences” (Rock & Pollack, 2002).1
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.
To make it easier to interpret the results, Figure 1 below shows the average number of questions answered correctly by kids on the first-stage assessment. Kids are organized by household income status (quintiles). The chart shows results at three points in time: fall kindergarten, spring kindergarten, and spring first grade. Kids in the bottom group on average answer about 3 correct (out of 12) in fall kindergarten. By contrast, kids in the top group on average answer nearly 7 questions correctly. There are clear gaps in the average performance of kids in each socioeconomic group. (Mouse over the chart.)
Figure 1. General knowledge about natural science and social studies concepts.
By the end of kindergarten, both the top and bottom socioeconomic groups average one more correct question — maintaining the 4 question gap. This gap narrows slightly by the end of first grade. However, the average of 6.5 correct answers for kids in the lowest socioeconomic household in spring of first grade is roughly equivalent to that of the highest socioeconomic group in the fall of kindergarten. The overall pattern of gaps between socioeconomic groups remains unchanged.
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.
Figure 2. Counting beyond ten and ability to compare size of different objects.
This next chart shows a similar growth pattern for a constrained reading skill—letter-sound correspondence at the end of words. Again, there were early and significant proficiency gaps at school entry. By the end of first grade, however, these gaps had significantly closed. All groups were over 90% proficiency, with all but one within a few percentage points of 100% average proficiency.
Figure 3. Ability to associate letters with sounds (letter-sound correspondence) at the end of words.
The relationship between knowledge, reading, and mathematics
Supporting children’s world knowledge is important in its own right. It’s also connected to their reading and math skills. The ECLS-K researchers found moderate correlations between scale scores for general knowledge and K-1 scale scores for reading and math (Rock & Pollack, 2002). The correlations between general knowledge and reading were fairly stable from fall kindergarten through spring first grade (between 57% and 59%). The same was true for general knowledge and mathematics (between 64% and 67%).
Kids need opportunities to develop general knowledge
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.
Rock and Pollack (2002) made this observation in a technical manual for the ECLS-K:
It is interesting to note that gains from a full year of schooling (fall to spring, in both kindergarten and first grade) in terms of standard deviation units [(i.e. the spread of individual scores from the average)] on general knowledge appear to be considerably less than those that were demonstrated in both reading and mathematics. Also, there is less differential in growth rates exhibited between adjacent [testing] rounds than in reading and mathematics. The rate of growth during the summer between kindergarten and first grade is closer to the growth during the school year intervals than was found in reading and mathematics. It would appear that the general knowledge test is measuring information that is not necessarily included in most kindergarten and first-grade curricula but is associated more with the child’s out-of-school experiences. [Emphasis added.]
These differences in opportunity are made more plain by examining differences in general knowledge across socioeconomic levels within a single racial group. This next chart shows correct responses to the first-stage general knowledge questions by Black students across five socioeconomic groups.
Figure 4. General knowledge about natural science and social studies concepts.
The initial pattern at kindergarten entry is a little different than for the full sample in Figure 1. Black kids from the three highest socioeconomic levels average roughly the same correct number of questions (3.6 to 3.8). By spring of kindergarten this bunching between the higher income groups is erased. We see the same stair-step pattern that exists in the full sample. This pattern repeats in spring of first grade.
There is more current use 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.
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.
Paris, S. G., Carpenter, R. D., Paris, A. H., & Hamilton, E. E. (2005). Spurious and genuine correlates of children’s reading comprehension. In S. Paris & S. Stahl (Eds.), Children's Reading Comprehension and Assessment (pp. 149-178). New York: Routledge.
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.
Snow, C. E., & Kim, Y.-S. (2007). Large problem spaces: The challenge of vocabulary for English language learners. In R. K. Wagner, A. Muse, & K. Tannenbaum (Eds.), Vocabulary acquisition and its implications for reading comprehension (pp. 123–139). New York, New York: Guilford.
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.
The K-1 general knowledge test was evaluated and found to be free from bias by socioeconomic status (Rock & Pollack, 2002). In third, fifth, and eighth grades, a science assessment replaced the general knowledge assessment.