A kindergarten educator reviewing intake assessments at the start of the school year sees the data before she meets the children. The data tells part of the story, but they don’t say whether the preparation those children received was grounded in evidence and supported through intentional curriculum implementation or simply in tradition. Fortunately, independent research can now tell educators how prepared children are for the next step. That is why independent research matters. It gives educators, district leaders, and decision-makers a clearer way to understand whether a curriculum is connected to measurable kindergarten-readiness outcomes in real classrooms.
The challenge is that most evidence about the curriculum is produced by the companies that sell it. That’s not always a problem, but it does mean that when an independent institution publishes a study, it carries a different weight. A superintendent can bring a Johns Hopkins University finding to a school board with greater confidence because the source is external to the curriculum provider.
Boards wonder whether investing in Pre-K moves children forward. Independent research suggests that high-quality Pre-K curriculum implementation can make a measurable difference. Published in May 2026 and conducted in a large, diverse public school district under real classroom conditions, the Guilford County efficacy study examined kindergarten-readiness outcomes for children in Guilford County Schools using the Frog Street Pre-K curriculum.
The findings do not suggest that every district will produce identical results. Implementation, staffing, student population, and local context always matter. What the study does provide is a credible, independently conducted reference point for understanding what happened when Frog Street Pre-K was implemented in real public-school classrooms.
Key Findings At A Glance
| +0.26
Effect size Overall kindergarten readiness |
~10
Percentile gain Gain at kindergarten entry |
+0.62
English learning effect Larger observed subgroup effect |
+0.31
Physical development Statistically significant |
Source: Grant, Cook & Ross (2026), Johns Hopkins University CRRE. Study conducted in a large, diverse district under real classroom conditions.
What Did The Johns Hopkins Study Find?
The study followed children who attended Guilford County Schools PreK classrooms using the Frog Street PreK curriculum in North Carolina into their kindergarten year. Guilford County is the third-largest school district in the state, serving about 67,000 children across 124 schools, and the study focused on the cohort of children who attended PreK in 2023 to 2024 and entered kindergarten in 2024 to 2025.
Families applied to the broader NC Pre-K program in Guilford County rather than to a specific curriculum program, and families were unaware of curriculum assignment during site selection. Placement decisions considered both demonstrated need and family site preferences.
Researchers compared 223 Guilford County children in classrooms using the Frog Street Pre-K curriculum across 9 schools to 641 Guilford County children in classrooms using another preschool curriculum across 41 schools, using the North Carolina Early Learning Inventory to measure readiness. The study also controlled for the fact that children were not randomly assigned to classrooms, which is a common challenge in real-world school research. The study also notes that instructors using Frog Street PreK were in their first and second year of implementation during the study period.
The study found that children who attended Guilford County classrooms using the Frog Street Pre-K curriculum scored statistically significantly higher on the NC-ELI composite at kindergarten entry. The effect size was +0.26, which Johns Hopkins described as educationally meaningful.
The raw score advantage was +0.37 NC-ELI points. The study also found positive gains across all five developmental domains measured by the NC-ELI, not just one. For boards considering the value of Pre-K, this study provides one independently conducted example of how curriculum implementation may support multiple areas of kindergarten readiness under real classroom conditions.
What Does a 10 Percentile Gain Mean In Practice?
Effect sizes are useful to researchers. They’re less useful to a curriculum director who needs to explain a curriculum decision to a parent or a school board.
So here’s the translation: a child who would have scored at the 50th percentile on kindergarten readiness tests would score closer to the 60th percentile after attending a Pre-K class using the Frog Street Pre-K curriculum. That’s approximately a 10 percentile gain over what you’d expect from the comparison curriculum. For a curriculum serving 100 children, that makes a meaningful difference. That does not mean every child will move exactly 10 percentile points. It means the observed effect size can be translated into a practical estimate that helps leaders understand the magnitude of the finding.
What Did The Study Find For Children Learning English?
Children learning English in Guilford County classrooms using the Frog Street Pre-K curriculum showed an effect size of +0.62, indicating a larger observed difference within that subgroup and statistical significance at p < .001.
That finding matters for several reasons. The study population reflected a diverse, multi-ethnic district, and the English learner (ELL) subgroup, while smaller than the overall sample, still demonstrated statistically significant outcomes within the context of the study.
Johns Hopkins found that English learners in Guilford County classrooms using the Frog Street Pre-K curriculum showed stronger kindergarten-readiness outcomes compared with English learners in the comparison group. While results can vary across districts and implementation settings, this finding may be relevant for leaders evaluating curriculum support for children learning English as a second language.
For funding and evaluation conversations, this point matters. Districts and early childhood programs are often asked to show how curriculum decisions support children with diverse language backgrounds. This study provides one independently conducted evidence point that may help inform those discussions.
| Download the Research Summary for Leaders
Full findings, plain-language effect size explanations, and ESSA documentation in one place. |
What Do The Domain-Level Outcomes Mean for Everyday Classroom Experience?
The NC-ELI measures five developmental domains: Language and Literacy, Mathematics, Cognitive Development, Social-Emotional Development (SED), and Physical Development. Guilford County children using the Frog Street Pre-K curriculum showed positive gains across all five. The domain with a statistically significant finding was Physical Development, with an effect size of +0.31 and a p-value of less than .01.
Physical Development isn’t the first domain people mention when they talk about kindergarten readiness. But for educators who understand developmental sequencing, it makes sense. Fine motor control, gross motor coordination, and physical self-regulation are tied directly to a child’s ability to hold a pencil, sit at a table, navigate transitions, and participate in the full range of classroom activities. A curriculum that builds physical development alongside language and math is doing what developmental science says it should.
For educators implementing the Frog Street Pre-K curriculum, these domain-level findings reflect what the curriculum is designed to do: weave together cognitive, language, physical, and social-emotional development (SED) across every lesson and routine. The research confirmed what intentional, consistent implementation can produce when the curriculum is used as designed.
How Does This Study Compare to Other Early Childhood Curriculum Research?
Most curriculum evidence in early childhood education falls into one of two categories: internal studies produced by the company itself, or literature reviews that do not test the curriculum directly. The Guilford County study is different. It is an independent, third-party study that compared children in Guilford County classrooms using the Frog Street Pre-K curriculum with children in Guilford County classrooms using another preschool curriculum implemented across 41 schools.
The study also received ESSA Tier 3 Promising Evidence designation, assigned by the study’s own authors at Johns Hopkins. That is not a label Frog Street applied. It means the research methodology meets the federal evidence standard used in Title I funding documentation, Head Start curriculum expenditure justifications, and state early childhood grant applications. For leaders who need to justify curriculum decisions to funders or state reviewers, ESSA Tier 3 alignment provides a recognized evidence framework.
Other research also helps contextualize the Guilford County study. The American Institutes for Research independently confirmed the Frog Street Pre-K curriculum’s alignment with research-based practices and early learning standards. The Massachusetts Department of Early Education and Care curriculum review report evaluated Frog Street Pre-K across four domains in August 2024, with five independent reviewers scoring it between 3.5 and 3.7 out of 4.0 on each.
Together, these sources provide multiple forms of evidence that may support curriculum evaluation discussions. The Johns Hopkins study speaks to outcomes. AIR speaks to alignment with research-based practices and standards. The Massachusetts review speaks to external curriculum quality ratings. For decision-makers, these sources can contribute to a more comprehensive evaluation.
Why Does It Matter That This Was a Real District With Real Classrooms?
Controlled research environments can produce cleaner data, but they may also create findings that are more difficult to apply to everyday educational settings. The Guilford County study was conducted in real public-school classrooms, with educators implementing curriculum under typical district conditions.
The study took place in Guilford County Schools, where the Frog Street Pre-K curriculum was being implemented during the study period. Families applied to the broader NC Pre-K program in Guilford County rather than to a specific curriculum program, and placement decisions considered both demonstrated need and family site preferences.
The study also notes that instructors using Frog Street PreK were in their first and second year of implementation during the study period.
That context matters because curriculum decisions are made within real systems, not controlled environments. Leaders need to understand how evidence relates to the complexity of actual classrooms, including staffing variation, student diversity, implementation realities, and district conditions.
A real district study can help answer a practical question many boards and decision-makers ask: what happened when the curriculum was used under authentic classroom conditions in a large public-school district?
Frequently Asked Questions
What is the Guilford County efficacy study?
The Guilford County efficacy study is an independent research study conducted by the Johns Hopkins Center for Research and Reform in Education, published in May 2026. It examined the impact of the Frog Street Pre-K curriculum on kindergarten readiness in Guilford County Schools, North Carolina, comparing 223 Guilford County children in classrooms using the Frog Street Pre-K curriculum across 9 schools to 641 Guilford County children in classrooms using another preschool curriculum across 41 comparison schools.
What does a +0.26 effect size mean for kindergarten readiness?
An effect size of +0.26 translates to approximately a 10 percentile gain at kindergarten entry. A child who would have scored at the 50th percentile in readiness moves to roughly the 60th percentile after participating in the Frog Street Pre-K curriculum. Johns Hopkins describes this as a large, educationally meaningful impact.
What did the study find for children learning English?
Children learning English taught with the Frog Street Pre-K curriculum showed an effect size of +0.62 on the NC-ELI composite at kindergarten entry. That represented a larger observed difference within the subgroup and statistical significance at p < .001. The study was conducted in a diverse, multi-ethnic district, which may make this finding relevant to curricula serving multilingual communities.
What is ESSA Tier 3 Promising Evidence, and why does it matter?
ESSA Tier 3 Promising Evidence is a federal evidence designation assigned by the study’s own researchers at Johns Hopkins, not by Frog Street. It means the research meets the standard required for Title I funding documentation, Head Start curriculum expenditure justifications, and state early childhood grant applications.
Where can I access the full Johns Hopkins study?
You can download the complete study report at the Frog Street kindergarten readiness research report page, with no form required. The ESSA Tier 3 certificate is also available for download.
The research exists, but it can be challenging to get this information in front of educators and leaders who make curriculum decisions. Check out the Educator Research Summary to understand how these findings translate for leaders and classroom educators.
Leaders who download the Educator Research Summary walk away with plain-language findings they can share with families and a research stack they can take to a board or funder. The goal is to help leaders and educators better understand how independent research findings may inform curriculum evaluation conversations.
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Plain-language findings, domain-by-domain results, and language for family conversations. |
