New research from the Center for Global Development shows that standardised effect sizes promise comparability but often don’t deliver it. It proposes that researchers report raw effects and reference distributions alongside standardised estimates as a best practice.
In 2021, an evaluation in East Africa reported reading and writing effect sizes that the authors described as “comparable to some of the largest measured in the literature”: 0.64 and 0.45 standard deviations (SD). In education research, this is considered a “large effect size,” and by this measure, the programme appears to have achieved landmark success improving children’s literacy skills.
The 0.64 SD effect on reading corresponded to a raw gain of only 1.8 additional correct words per minute. This modest improvement in reading translated into a large effect size only because the group they were being compared to made so little progress: 96 percent of children in control schools could not read a single word at endline.
Matthew Jukes, Senior Director of Impact, The Luminos Fund
Reporting standardised effect sizes as the headline figure for a study’s impact is standard practice. It provides a common metric to compare programs using different assessment tools implemented in different contexts. But, as described in a new paper by Jack Rossiter, David Evans, Susannah Hares, and Catherine Henny—which cites the East African example above—standardised effect sizes, reported in isolation, often tell us very little about what children actually learned.
Standardised effect sizes, reported in isolation, often tell us very little about what children actually learned.
The Exchange-Rate Problem
Effect sizes measure the magnitude of an intervention’s impact in standardised units. They are calculated by dividing the raw gain in scores from baseline to endline by the standard deviation, a measure of how much individual scores vary.
Because the standard deviation depends on the spread of scores in a comparison group, the same real-world learning gain (such as one additional word read per minute) can produce very different effect sizes. This means effect sizes are not the neutral cross-study currency researchers treat them as.
The Rossiter et al. paper demonstrates this with oral reading fluency data. Across 66 study-language-grade combinations, an improvement of just one correct word per minute is worth anywhere from 0.03 to 0.55 SD. The same learning gain can look up to seventeen times bigger in one study than another.
In low-literacy settings, where many children score zero, the distribution of scores is so compressed that even very small raw gains produce large effect sizes.
Effect sizes are a useful tool. The problem is reporting them without enough context to understand what children can actually do differently as a result of the programme.
Can the Children Read?
As the paper proposes, the fix is to report interpretable outcomes alongside standardised effects—to say whether children can now do the things that matter for learning to progress.
In some areas this is genuinely hard. Oral reading fluency benchmarks vary across languages and scripts, and calibrating them sensibly takes real work. But that complexity shouldn’t obscure a simpler point: many early reading skills are perfectly interpretable without benchmarks at all.
Many early reading skills are perfectly interpretable without benchmarks at all.
For instance, children need to know the sounds represented by the letters of the alphabet reliably before they can move on to more advanced skills. A programme can report exactly what share of children have reached that threshold, rather than leaving readers to decode a standard deviation.
Reporting interpretable outcomes also tells you what children are ready to learn next. A child who has mastered foundational skills such as letter-sound knowledge is ready to begin decoding words. One who can decode accurately but haltingly needs additional fluency practice. One who can read connected text with some ease is ready for a stronger focus on comprehension.
Knowing where children fall along this progression tells us clearly what they have learned, what support they may need next, and whether a programme is effectively doing its job.
In a Grade 2 literacy programme, the key question is whether children have reached the level needed to benefit from Grade 3 instruction. In an accelerated learning programme, it is whether students are ready to re-enter mainstream schooling. A standard deviation cannot answer either question.
This kind of reporting is absent from a large share of published quantitative work on literacy.
What We See in Our Own Data
The Luminos Fund runs accelerated learning programmes that enable vulnerable and out-of-school children to cover three years of learning in one year. An independent randomised controlled trial (RCT) of the Luminos programme in Liberia found large effects of 1.2–1.4 SD on reading. In Ethiopia, a government-run accelerated learning programme implementing the Luminos model improved reading by 1.4 SD.
But it is in the raw data where the meaning sits.
Across our programmes in Liberia, Ghana, and Ethiopia in 2024–25, students entering with minimal prior schooling left scoring around 90 percent on a letter sounds task. Average oral reading fluency gains ranged from 22 to 47 correct words per minute across programmes, moving students from non-readers to readers of connected text in a single school year. In Liberia, students progressed from reading just 4 correct words per minute at baseline to 51 by endline—4.6 times the 2016 average for primary school-age children in the country.
Explore our Results
Independent evaluations of the Luminos programme in Ethiopia, Ghana, Liberia, and The Gambia during the 2024–25 school year show children who entered Luminos classrooms unable to read even a single word are now reading full sentences and solving math problems with confidence.
In reading comprehension, scores on five-item comprehension tasks ranged from roughly 25 to 45 percent, up from near zero at baseline in every case.
We are pleased with these gains, though getting all children to understand what they read in a single year remains the harder challenge—particularly for children building comprehension in a language they don’t speak at home.
Effect sizes offer a measure of comparability; raw scores give us interpretability. That is the standard the field should hold itself to.
In each case, the gains in students’ literacy skills are simple to describe and easy to interpret. Effect sizes offer a measure of comparability; raw scores give us interpretability. That is the standard the field should hold itself to.
When a programme claims to have improved learning, it should be able to answer a basic question: what can children do now that they could not do before?
Luminos students in Liberia work on a literacy assignment in their notebooks writing vowel letters.(Photo: John Healey for the Luminos Fund)
Matthew Jukes is Senior Director of Impact at the Luminos Fundwhere he oversees data systems and strategy to support program impact measurement, implementation, and maintenance. He plays a key role in ensuring data quality and in sharing data across the organization to inform Luminos’ programming and decision-making.
Luminos Fund supported the independent research paper discussed in this blog.
Reading is the foundation of all education. It serves as a gateway to acquiring new knowledge, fosters critical thinking, and opens doors to lifelong learning and personal growth. Despite significant progress in improving access to schooling, nearly 7 out of 10 children in low- and middle-income countries (LMICs) cannot read a simple, age-appropriate text by the end of primary school. In my role as Associate Director of Teaching and Learning at the Luminos Fund, ensuring students learn to read is one of my main priorities.
A study I co-authored along with Dr. Kathy Rastle, Michael Crawford, and Maria Korochkina, published in Nature Human Behaviour, highlights the failure of education systems in LMICs to teach children to read.
Neha Raheel, Luminos Associate Director of Teaching and Learning
Findings from 230 Early Grade Reading Assessment (EGRA) surveys across 48 countries, 96 languages, and over half a million students reveal that most children are not acquiring even the basic foundations of literacy.
However, bridging the literacy gap is possible. Evidence gathered over the past two decades from the science of reading suggests that all children can learn to read, provided they receive high-quality, systematic, and explicit phonics instruction. At the Luminos Fund, our approach to literacy focuses on teaching children how to decode using systematic phonics. We provide explicit instruction on the relationships between sounds and letters, enabling children to decode new words instead of simply memorizing them. This critical skill empowers children to move from learning to read to reading to learn, unlocking their full potential.
Challenges in Early Literacy: The Need for Phonics Instruction in LMICs
Decoding is the ability to translate a word from print to speech using knowledge of the relationships between letter sounds and symbols. Several studies show a clear link between reading with meaning (reading comprehension) and decoding skills. Yet, most children in LMICs struggle with basic skills, like identifying the names and sounds of letters and blending sounds to read words – essential building blocks of reading.
National curricula and assessment frameworks in LMICs often focus on reading comprehension but do not explicitly emphasize the need for systematic phonics instruction. It is not surprising, then, that even by the third year of schooling, 96% of students in our study fall below the severe-risk benchmark for identifying letter sounds. These students face a high risk of reading failure and require intensive support beyond the core curriculum.
While the study analyzes literacy scores of students in mainstream schools, the learning crisis is even more dire for the nearly 251 million out-of-school children around the globe. More than half of the world’s out-of-school children are in Sub-Saharan Africa, where prior to the COVID-19 pandemic, 86% of children could not read or understand a simple text by age 10.
The Luminos accelerated learning program helps vulnerable, out-of-school children in Sub-Saharan Africa build foundational reading and math skills. This enables them to catch up to their grade level, reintegrate into mainstream schools, and prepare for lifelong learning. Our literacy approach is centered on explicit and systematic phonics instruction, teaching children the relationship between sounds and letters and how to blend letter sounds to decode words. To ensure learning is both effective and joyful, Luminos makes phonics instruction engaging and culturally relevant by incorporating local stories, songs, games, and activities that resonate with children’s experiences. This explicit approach to literacy instruction is especially important for children who have never attended school, are the first in their families to learn to read or are learning to read in a language they do not speak at home – common challenges in the communities where we work.
Luminos teacher Sekou leads the class in breaking down green words into Elkonin sound boxes. (Photo by Mara Chan/Luminos Fund)
To further support instruction, Luminos uses a structured pedagogy approach, providing high-quality and contextually relevant teaching and learning materials, teacher training, ongoing support, and regular assessments of students. Additionally, external evaluators assess students’ literacy and numeracy twice during the year using EGRA and Early Grade Mathematics Assessment (EGMA).
As a result of our explicit and systematic phonics approach, Luminos students consistently outperform their peers in mainstream schools. By the end of the 2023-24 school year, Luminos students in Liberia could, on average, identify 73 correct letter sounds per minute (CLSPM) and students in Ethiopia could identify 70 correct letter sounds per minute – far exceeding early literacy benchmarks for Grade 3 according to the Dynamic Indicators of Basic Early Literacy Skills (DIBELS).
Additionally, Luminos students in Liberia could correctly identify 88 letter names per minute, which is well above the Grade 2 benchmark goal of 53. According to DIBELS, students who score above the benchmark are at minimal risk of reading failure and can succeed with the core curriculum. In stark contrast, 96% of students sampled in our study on LMICs fell below this benchmark for letter sound identification by the third year of instruction.
This success demonstrates the adaptability of the Luminos program across diverse LMIC contexts, such as Liberia and Ethiopia, where a phonics-based approach continues to improve reading outcomes despite differences in writing systems. In Ethiopia, for instance, we teach in languages with alpha-syllabic writing systems, such as Sidaamu Afoo, Afaa Xonso, and Tigrinya, whereas in Liberia, we teach in English (an alphabetic writing system). These results demonstrate Luminos’ potential to drive long-term, systemic change, and provide a scalable model for improving foundational literacy. By equipping children with the skills and confidence to read, Luminos not only empowers them but also contributes to broader efforts to close the global literacy gap.
Our study in Nature Human Behaviour underscores the importance of prioritizing decoding skills through systematic phonics instruction as the foundation of literacy. Without mastering these foundational skills, ensuring that all children can read with comprehension remains a distant aspiration.
To address the learning crisis and set children on a path to lifelong learning, we call on educators, policymakers, donors, and partner organizations to focus on developing these critical skills. By adopting evidence-based methods for reading instruction, we can ensure that more children achieve key early literacy milestones, ensuring their future academic success. Together, we can give every child the opportunity to unlock the transformative power of reading and build a brighter future.
Students in The Gambia raise one finger for the first sound they hear when breaking down a word into sound boxes. (Photo by Lena Nian for the Luminos Fund)
Neha Raheel is Associate Director of Teaching and Learning at the Luminos Fund, where she is responsible for the development of high-quality teaching and learning materials. She designs and delivers impactful trainings, and builds the capacity of colleagues and partners to help every child to learn. Prior to joining Luminos, Neha worked at the World Bank, where she supported the Education Global Practice team on curriculum, instruction, and learning, focusing on foundational learning. Neha is a Fulbright scholar and holds an MS.Ed in Education, Culture, and Society from the University of Pennsylvania, and a BA in Humanities from the Lahore University of Management Sciences. In 2020, she was selected as a WISE Emerging Leader, in recognition of her contributions to the field of education.
There is nothing like a child’s joy when they discover that all the world’s knowledge is available to them because they can read and write. It unlocks the light within and gives them a sense of freedom and opportunity. It compels them to want to learn all they can about our planet – its places, peoples, possibilities, and even problems. It inspires them to keep on learning – whenever they can and for as long as they can – as they strive to make a meaningful contribution to society throughout their lives.
We call this experience “joyful learning”, and we believe it’s something every child deserves. The unfortunate reality is that there are still millions of children worldwide who do not get a chance to learn at all. This is an injustice and an inequality that needs to be addressed. That’s why Luminos exists. We’re here for children like Mary in Liberia and Ahmed in Lebanon, who have faced barriers related to poverty, conflict, and discrimination that have delayed their opportunity to learn.
With your incredible support, however, Luminos has been able to step into the gap and provide a second chance to children like Mary and Ahmed. We are thrilled to be able to work with our dedicated network of implementing partners, committed investors, and thoughtful experts, who have helped bring joyful learning opportunities to life for these children in Ethiopia, Liberia, and Lebanon. Over the next three years, with your help, we will not only expand opportunities in these countries, but also bring joyful learning to children in other locations as well.
The recognition for our programs over the last year has been deeply humbling. We are honored and delighted to have received the WISE Award from the Qatar Foundation and the HundrED Global Innovations Award. It is a tribute to the hard work our children and their learning facilitators have put into their learning. We are so very proud of them!
In the coming years, we want to play a role in improving the information available to education decision-makers, encouraging more collaborative action, facilitating experimentation, and supporting evidence-based systems change as we work together to make joyful learning available to all children.
We look forward to your partnership as we progress in this critical journey. Thanks for your continuing support!
