Constrained and unconstrained skills—so what?
What academic researchers say about constrained and unconstrained skills.
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 summarizes the impact that constrained skill theory has had on academic research. The title is a callback to a 2008 address by Scott Paris, “Constrained skills—so what?”, who published the first paper on constrained skill theory 20 years ago. Like everything on this Substack, this post is a work-in-progress. I will make updates as needed. Citations are included at the end. Questions, comments, and suggestions are welcome.
Last updated: August 30, 2025
Three big ideas
Constrained skill theory is one of the most influential ideas proposed over the past 20 years among academic researchers in education.
For at least 15 years, academic researchers have called for more explicit focus on building kids’ unconstrained skills to improve reading and math achievement.
Academic researchers to date have proposed that consideration of differences between constrained and unconstrained skills have implications for family engagement, Pre-K programs, educational apps, curricula, assessments, and interventions.
An influential idea in education research
A 2014 article in the journal Nature observed that less than 1% of academic papers receive 1,000 or more citations in other academic publications (Van Noorden et al., 2014). Just 100 citations gets a paper in the top 2% overall. According to Google Scholar, the three articles that often get cited for constrained skill theory — Paris (2005), Stahl (2011), and Snow and Matthews (2016) — currently have over 1,200, 140, and 350 citations, respectively. For academics, this is rare air. This signifies the influence that constrained skill theory has achieved among academic researchers over the past 20 years.
Advocacy for policy and practice change
Academic researchers use the constrained skill framework to advocate for change in education. Here are some examples:
Stahl (2011) advocates for educators to provide due attention to both constrained and unconstrained skills in classrooms. “Teaching constrained skills explicitly and systematically and matching instruction to students’ developmental needs should ensure that the largest portion of the literacy block can be allocated to the more complex unconstrained abilities throughout the elementary years.”
Snow and Matthews (2016) similarly call for more focus on unconstrained skills in classroom instruction. “[M]any prekindergarten through third-grade classrooms, particularly those serving low-income children, still focus on constrained skills, which are easy to teach and easy to test. Ensuring that teachers pay appropriate attention to unconstrained skills in early childhood and primary classrooms is a serious challenge.” They contended that declines in literacy scores on the NAEP between elementary to middle school “suggests that our schools may be focusing too much on constrained skills—and too little on unconstrained ones—in the early grades.”
Dennis (2017) uses the constrained skill framework to reflect on education policy and practice under No Child Left Behind. She notes that curriculum, interventions, and assessment during the Reading First era heavily focused on constrained skills in isolation. Dennis advocates for a different approach under the newly passed Every Students Succeed Act that incorporates both constrained and unconstrained skills.
Pianta et al. (2021) argue that Pre-K “fadeout” in early elementary school is due to catch-up in constrained skills by children who do not attend Pre-K programs. They call for greater focus on instruction in unconstrained skills in Pre-K programs to make them more effective and their benefits longer-lasting in elementary school.
McCormick and Mattera (2022) note a pattern in evaluation of Pre-K programs in which children who did not attend pre-K quickly develop constrained skills and catch up to their peers in elementary school. They call for including unconstrained skills in Pre-K assessments to provide a fuller picture of the impact of Pre-K programs. They acknowledge the relative ease of assessing constrained skills compared to unconstrained skills, but hold out hope that advances in technology could yield potential solutions to overcome this challenge.
Whittingham et al. (2024) raise concerns about what they see as a disproportionate focus on constrained skills within the “science of reading” movement. They describe correlational, longitudinal, and meta-analytic studies that demonstrate the interrelationships between constrained and unconstrained skills. They raise concerns about consequences for children from disadvantaged households if they don’t receive adequate opportunities to build unconstrained skills like vocabulary and writing. They call for a more expanded view of the “science of reading” that incorporates both constrained and unconstrained skills within curriculum, assessment, instruction, and interventions.
Hadley et al. (2025), summarizing the negative impact of COVID-19 on the unconstrained literacy skill development of children in early elementary school, advocate for multi-component literacy interventions for these children that “provide instruction on both code-focused constrained skills and language-focused competencies such as background knowledge, vocabulary, and inferencing.”
Hanno et al. (2025) call for greater breadth and depth of measured skills in direct child assessments. They explicitly call for greater inclusion of unconstrained skills: “Overcoming the complexities of capturing unconstrained skills is central to fostering stronger pedagogical practices that build on children's strengths and identifying programs that are most effective in promoting these important skills. One way to deepen domain measurement to include more unconstrained skills is to align assessment content to developmental trajectories rather than focus on discrete skills.” The authors acknowledge the practical implications and current limitations. They hold out the prospect of technology-based solutions, such as artificial intelligence (AI), to make greater and deeper assessment of unconstrained skills possible.
Research into effects on student achievement
Researchers in recent years published studies about the relationship between constrained and unconstrained skills and student achievement:
McCormick et al. (2020) conducted an experimental study with 307 parents of Pre-K children to evaluate the relationship between constrained and unconstrained skill activities at home and Pre-K classroom reading and math achievement. They find that unconstrained language activities at home predicted student gains in language skills in the classroom. Unconstrained math activities at home also contributed to improvement in classroom math skills. In fact, the impact of unconstrained skill activities at home on language and math gains in the classroom is greater for families with lower levels of parental education. Conversely, the study does not find a significant relationship between constrained literacy or math activities at home and growth in constrained skills in the classroom.
McCormick et al. (2021) conducted an experimental study with just over 500 children in public and nonpublic Pre-K programs in Boston. The children, who attended Boston Public Schools, were followed through the spring of kindergarten. The researchers find stronger sustained benefits of participation in the BPS public prekindergarten program on student’s unconstrained language and math skills in the spring of kindergarten. They also find sustained benefits of participation in non-public Pre-K programs on unconstrained language skills (but not math skills) through the spring of kindergarten. Overall, the sustained benefits of Pre-K participation by the end of kindergarten are greater for unconstrained skills than constrained skills.
Kim et al. (2021) evaluated 36 studies and nearly 300 outcomes on the effectiveness of educational apps for Pre-K-3 children on constrained and unconstrained reading and math skills. The paper notes that “one-to-one tutoring, small-group instruction, and whole-classroom interventions typically have their largest impact on constrained skills such as letter knowledge, print awareness, and phonemic awareness in literacy and counting, sorting shapes, and simple sums in math.” Controlling for assessment type and student grade level, they find that like these other types of support, education apps also make greater gains on constrained skills. In fact, the impact of education apps on constrained skills is more than twice as large as unconstrained skills.
Ansari et al. (2023) analyzed just over 2,300 students in a large and diverse county in Virginia. This study uses the constrained skill framework to review the patterns of reading, math, and executive skill convergence in kindergarten and first grade between students who attended and did not attend Pre-K programs. Students who attend Pre-K started kindergarten with stronger early literacy (knowledge of letters and words, expressive vocabulary), math (facts and concepts), and executive skills (working memory, inhibition control, attention). The researchers find these advantages decline by 55%-60% by the end of kindergarten. In the spring of kindergarten they find that Pre-K attendees no longer hold advantages over non-attendees on letter-word identification (a constrained skill). In other words, most of the “fadeout” for this constrained skill occurs in kindergarten. However, for more unconstrained skills of expressive language and executive function, “catch up” by children who did not attend Pre-K occurs more evenly across both kindergarten and first grade.
Johnson et al. (2023) analyzed the sustained benefits of Pre-K participation on a range of outcomes: language, literacy, math, and executive function. This study explicitly used the constrained skills framework but appears to only apply it to language and literacy skills. The paper analyzed just over a 1,000 students in Tulsa Public Schools from Pre-K through first grade. The quasi-experimental study used child and family background characteristic to create propensity score weights to account for the probability of attending Pre-K (the “treatment” group) or not (the “comparison” group). The study had two “treatment” groups: one who attended school-based Pre-K and one who attended Head Start. The researchers found enduring benefits of Pre-K participation by the end of first grade for two unconstrained literacy skills — expressive vocabulary and sentence structure. They found no enduring benefit by the end of first grade for letter-word identification (constrained). They did find, however, a continued benefit of Pre-K participation for phonological awareness, a moderately constrained skill.1 The researchers found no additional benefit of Pre-K participation on executive skills in kindergarten or first grade.
McCormick et al. (2025) evaluated growth in language, literacy, math, and executive function skills for 422 students in Boston Public Schools from kindergarten through first grade. This study uses the constrained skill framework to analyze patterns of convergence in skill proficiency between students who attended Pre-K and those who did not. Overall, the benefits of PreK participation on language and math skills were sustained through first grade. However, there were differences in convergence (i.e. “fadeout” or “catchup”). More convergence between PreK enrollees and non- enrollees in language skill ability occurred during first grade than kindergarten. Conversely, greater convergence in math skills occurred during kindergarten than in first grade. By contrast, the researchers found no enduring additional benefits of PreK participation on executive function skills by spring of first grade. Most of the convergence (“catchup”) between Pre-K participants and non-participants in executive skills occurred in first grade.
Hadley et al. (2025) compared two large cohorts of students from PreK through first grade to analyze the impact of the COVID-19 pandemic on student learning. This study explicitly used the constrained skill framework to evaluate two cohorts of over 1,000 students each that started Pre-K in the 2016-2017 academic year and another that started in the 2019-2020 academic year. The researchers found the negative impact of COVID-19 on unconstrained literacy skills was roughly double that of constrained literacy skills by the end of first grade. The researchers found these negative impacts on language and literacy were not moderated by child-level factors such as race, ethnicity, English language learner status, or poverty.
Thomas et al. (2025) conducted a quasi-experimental study with a literacy-focused educational application (AppLINOU) in 32 schools with just over 500 French students. The study explicitly used the constrained skill framework. The research was conducted over two years in Pre-K and kindergarten. The app contained 10 literacy activities that addressed both constrained (phonological awareness and letter knowledge) and unconstrained skills (vocabulary and listening comprehension). Students in experimental classrooms used the app for 20 minutes per week (two 10-minute sessions). Students in control classrooms experienced “business as usual” instruction. The intervention lasted for 10 weeks in the Pre-K year and 15 weeks in the kindergarten year. Teachers were given 10 hours of training but were allowed to integrate use of the app into their classrooms as they saw fit. The researchers found statistically significant effects for constrained literacy skills (letter knowledge and phonological awareness) but none for unconstrained oral language skills.
High-quality research always comes with careful caveats of the limitations of the studies. The study design also has important relevance. The research design of these studies include random experiments, meta-analysis, and correlational analysis. And some papers more explicitly use the constrained skill framework to test the impact of changes in practice than others.
But wait, there’s more
If you’d like to learn more about constrained and unconstrained skills, check out these other topics:
Constrained and unconstrained skills drive achievement in reading and math
A working list of constrained and unconstrained skills that support reading and math
An annotated summary of the major research papers behind constrained skill theory
Works cited
Ansari, A., Zimmermann, K., Pianta, R. C., Whittaker, J. V., Vitiello, V. E., Yang, Q., & Ruzek, E. A. (2023). The first-grade outcomes of pre-k attendees: Examining benefits as a function of skill type, environments, and subgroups. American Educational Research Journal, 60(6), 1139-1173.
Dennis, D. V. (2017). Learning from the past: What ESSA has the chance to get right. The Reading Teacher, 70(4), 395-400.
Hadley, E. B., Liu, S., Kim, E., McKenna, M., & Hull, K. (2025). Tracing the impact of COVID-19 on early language and literacy development from Pre-K through first grade. AERA Open, 11(1), 1–22.
Hanno, E. C., Portilla, X. A., & Hsueh, J. (2025). Designing equity-centered early learning assessments for today’s young children. Child Development Perspectives, 19(2), 92–98.
Johnson, A. D., Partika, A., Martin, A., Horm, D., Phillips, D. A., & the T. S. S. Team (2023). A deeper dive, a wider pool: Preschool benefits sustain to first grade on a broader set of outcomes. Child Development, 94(5), 1298–1318.
Kim, J., Gilbert, J., Yu, Q., & Gale, C. (2021). Measures matter: A meta-analysis of the effects of educational apps on preschool to grade 3 children’s literacy and math skills. AERA Open, 7(1), 1-19.
McCormick, M., Hanno, E., Weiland, C., Wu, T., Pralica, M., Hsueh, J., Giles, A., Snow, C., & Sachs, J. (2025). Moving beyond point in time estimates: Using growth models to understand when PreK convergence happens, how, and for which skills. Child Development, 96(4), 1354–1372.
McCormick, M., & Mattera, S. (2022). Learning more by measuring more: Building better evidence on pre-k programs by assessing the full range of children's skills. MDRC: New York, NY.
McCormick, M., Weiland, C., Hsueh, J., Pralica, M., Weissman, A. K., Moffett, L., ... & Sachs, J. (2021). Is skill type the key to the preK fadeout puzzle? Differential associations between enrollment in preK and constrained and unconstrained skills across kindergarten. Child Development, 92(4), e599-e620.
McCormick, M. P., Weissman, A. K., Weiland, C., Hsueh, J., Sachs, J., & Snow, C. (2020). Time well spent: Home learning activities and gains in children’s academic skills in the prekindergarten year. Developmental Psychology, 56(4), 710.
Pianta, R., Purtell, K., McCormick, M., Knoche, L., Burchinal, M., Ludvik, D. & Peisner-Feinberg, E. “Sustaining the pre-k boost: Skills type matters,” Spring (Lincoln, NE: Early Learning Network, 2021).
Snow, C. E., & Matthews, T. J. (2016). Reading and language in the early grades. The Future of Children, 57-74.
Stahl, K. A. D. (2011). Applying new visions of reading development in today's classrooms. The Reading Teacher, 65(1), 52-56.
Thomas, A., Hoareau, L., Jarlégan, A., Hubert, B., Luxembourger, C., & Tazouti, Y. (2025). Enhancing French preschoolers’ early literacy skills with a new educational classroom application. Early Education and Development, 36(4), 886–911.
Van Noorden, R., Maher, B., & Nuzzo, R. (2014). The top 100 papers. Nature, 514, 550-553.
Whittingham, C. E., Hoffman, E. B., & Paciga, K. A. (2024). Assessment, accountability, and access: Constrained skill mastery as instructional gatekeeper. Journal of Early Childhood Literacy, 24(1), 69-95.
The researchers in this study operationalized constrained and unconstrained skills as dichotomous (i.e. one or the other). However, multiple researchers — including Scott Paris himself — argue that skills fall along a continuum between more constrained and more unconstrained. Phonological awareness