The Error That Isn’t Random: What Students’ Mistakes Reveal About How We Teach

The Error That Isn’t Random: What Students’ Mistakes Reveal About How We Teach

By: Neha Raheel

Across sub-Saharan Africa, the learning crisis in foundational education is well-documented, but the conversation has largely centered on literacy. Although that focus is warranted—with roughly 70 percent of children in low- and middle-income countries unable to read a simple text by the end of primary school—numeracy deserves equal urgency.

Research consistently shows that early math skills are among the strongest predictors of long-term academic achievement. Children who leave primary school without secure number sense and arithmetic fluency face compounding disadvantages at every stage of schooling that follows.

Neha Raheel, Director of Teaching and Learning, Luminos Fund

Paying close attention to the common mistakes students make is one of the most powerful ways to improve how we teach.

At Luminos, we have spent years developing and refining structured numeracy materials for vulnerable and out-of-school children in Ethiopia, Ghana, Liberia, and The Gambia. Our programs build on proven teaching methods: explicit, systematic instruction; moving from concrete to pictorial to abstract representations to build understanding in deliberate stages before working with symbols; and regular assessments to keep learning on track.

Yet good frameworks alone do not guarantee learning. The challenge is ensuring that students truly grasp foundational concepts—and paying close attention to the common mistakes they make is one of the most powerful ways to improve how we teach.

Students in Ghana work out a math problem using stones and bottle caps during group work. (Photo by Mo Scarpelli for the Luminos Fund)

What Real-Time Data Can Reveal About Teaching

Our team routinely reviews classroom observation and student assessment data, analyzing patterns and asking what they reveal about learning progress. During one of these reviews in Liberia, a pattern emerged that stopped us in our tracks.

Internal data showed students performed well on foundational tasks but lost ground as arithmetic problems grew more complex; particularly addition and subtraction with three-digit numbers, regrouping numbers across place values, and understanding number sequences.

The Luminos Method: Real-Time Data

Real-time data drives classroom- and program-level decision-making for individual student impact, and is an essential component of the Luminos Fund’s accelerated learning program.

Taken individually, each of these gaps looks like a different instructional problem. Viewed together, however, they point to a common root: students needed a stronger understanding of place value.

Research on how children learn math is clear: lasting fluency isn’t just about knowing the steps to solve a problem, it depends on truly understanding the concepts behind them.

Understanding the Root Cause

Research on how children learn math is clear: lasting fluency isn’t just about knowing the steps to solve a problem, it depends on truly understanding the concepts behind them. A child may learn the steps for ‘carrying’ in an addition problem, but if they do not understand what those steps mean, the process can quickly fall apart. Carrying is not just moving a digit. It means exchanging ten ones for one ten because our number system is built around groups of ten. When students only memorize a procedure, their knowledge can be fragile. One unfamiliar problem format, or one forgotten step, and they may no longer know what to do.

Place value is one of the building blocks of early math. It helps children understand what a digit means based on where it appears in a number. It explains why a zero matters, why we carry or borrow when doing arithmetic, and how larger numbers work.

Without this foundation, students often rely on memorized rules rather than truly understanding the problem they are solving. Yet it is one of the most commonly underestimated gaps in early numeracy instruction. This is not because teachers fail to teach place value, but because students often encounter more complex arithmetic problems before they have had enough hands-on practice working with physical objects or pictures to really understand what each digit in a number means.

Our analysis in Liberia showed that the issue was not the lesson content itself, but how effectively teachers helped students grasp the underlying concepts.

Misconception:

Regrouping in addition is mechanical: students treat the the carried digit as just a “1”.

What it looks like:

A student learns to “carry the 1” in an addition problem without realizing that this “1” actually represents a ten. So they either forget to add it in the next column, or they add it but have no idea why.

Try this:

Trade 10 loose sticks for 1 bundle and say out loud: “I’m carrying 1 TEN, not just a 1.”  When writing it down, circle the carried digit as a visual reminder before adding the tens column.

Excerpt from the Luminos Foundational Numeracy Misconceptions Guide, 2026

Turning a Pattern Into a Resource

Our response was practical: we created a guide for teachers on common numeracy misconceptions and evidence-based strategies for addressing them. We designed it as a classroom tool rather than a theory document, to help teachers look beyond the wrong answer and understand the thinking behind it.

For each misconception, it asks three questions: What does the student actually believe? What misunderstanding is driving this error? And what can a teacher do, today, to address it?

A student who makes the same mistake repeatedly is showing you where their understanding broke down — not how little effort they are making. Diagnosing the specific misconception is the first step to helping them.

Luminos Foundational Numeracy Misconceptions Guide, 2026

We introduced the Foundational Numeracy Misconceptions Guide during teacher training in Liberia and the impact was immediate. We saw it in the quality of discussions during training sessions and, importantly, in how supervisors later described what they observed in the classroom. This is a mature program with years of implementation and iteration behind it. The fact that careful data analysis could still uncover opportunities for improvement is not a failure—it is exactly what a responsive system should do. Just as importantly, the solution was not redesigning our materials, but sharpening our focus on how we support teachers.

In Ethiopia and Ghana, classroom data revealed a similar pattern with missing number identification. In response, we adapted and translated the guide for use there, and we have already seen improvements in math scores across the board.

The guide will become part of our Teachers’ Guides for the upcoming academic year, signaling that what began as a targeted response to a data pattern has become a core part of how we train and support teachers across our programs.

Why This Matters

A growing body of research points to the importance of foundational numeracy. However, the sector has yet to develop the same shared practitioner vocabulary around diagnosing numeracy challenges that the science of reading brought to literacy instruction.

In many low-resource contexts, teachers receive training in what to teach but less support in recognizing the common misconceptions that predictably emerge, understanding what those errors reveal, and responding to them in the moment.

Access Our Materials

Great tools should be in as many hands as possible. Our classroom materials—including Teachers’ Guides, Student Books, and supplementary reading materials (Decodable Readers and Read Aloud stories)—are freely available. 

This matters because misconceptions in numeracy compound. A student who doesn’t understand place value will struggle with regrouping. A student who doesn’t understand regrouping will struggle with multi-digit operations. And a student who has only ever learned procedures, without understanding the ideas behind them, will find every new topic harder than the last; not because they are incapable of learning, but because they are building on a foundation that was never solid.

Sharing what we are learning is one way Luminos hopes to contribute to this conversation. We do not have all the answers, but we have found that the most useful insights come from paying close attention to what the data tells us and using it to ask better questions.

A student who has only ever learned procedures, without understanding the ideas behind them, will find every new topic harder than the last; not because they are incapable of learning, but because they are building on a foundation that was never solid.

What We Owe Every Child in the Classroom

I keep coming back to a particular kind of student: one who has been sitting in a classroom, trying their best, but making the same mistake week after week. Quietly, that student is concluding that math is not for them. That they are just not good at numbers. That something is wrong with them.

More often than not, the problem is not ability. It is understanding. The student was taught a procedure without being shown what it means. They were asked to memorize before they were allowed to understand. Over time, the gap between what they understood and what they were being asked to do became wide enough that they stopped trusting themselves.

Our job—as program designers, as trainers, and practitioners—is to close that gap. Not by moving faster or repeating instructions louder, but by asking: What does this child actually believe? Where did the understanding break down? And what, concretely, can we do about it today?

Those are the questions that guide our work. Behind every data point is a child sitting with a problem they cannot yet solve. What we owe them is not just better teaching materials: it is the curiosity to ask why, and the humility to let the answer change what we do next.

Neha Raheel is Director of Teaching and Learning at the Luminos Fund where she leads the development of high-quality teaching and learning materials grounded in the latest evidence from the science of teaching. She also designs and delivers impactful training on foundational learning and strengthens the capacity of colleagues and partners to help every child 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. 

How to Build Effective International Education Programs

How to Build Effective International Education Programs

Across the globe, access to universal education is often seen as a key goal for many international education programs — and it is tempting to think that learning follows a simple pattern: build schools, hire teachers, and children will learn.

Yet the fact that nine out of ten children in low-income countries cannot read by age 10 is proof that delivering effective education, especially in low-resourced settings, is hard.

Teaching children who are often the first in their families to learn to read is an extraordinarily daunting task — especially if doing so in a language they don’t speak at home, with minimally trained teachers, and little to no classroom materials. Adding to these challenges is the fact that many, if not most, of the international education interventions set up to improve school learning fail: currently, three out of five of the largest global funders of basic education have no evidence of impact at scale.

At the Luminos Fund, we know that effective education projects are rooted in iterative design – a process centered on continuous improvement and refinement. In this approach, organizations continuously evaluate their program implementation to assess their impact and make ongoing adjustments accordingly. For education projects and organizations, impact means students are learning, and the depth of that impact is the depth of a student’s learning gains.

Successful education initiatives marry the best of global learning science with local insights and apply an iterative approach to implementation. At Luminos, we have identified six key capabilities needed to create our organizational culture of iterative design:

1. A Deep Commitment to an Ongoing Journey

At Luminos, our iterative process is an ongoing cycle with three key stages: design, learn, adapt. From the moment our program is launched in the classroom, Luminos is iterating on our approach in response to the data we collect. Our learnings inform the nature, extent, and pace of our program adaptations. These adaptations occur across all aspects of our programming, including curriculum design, assessments, service delivery program support, and staffing capacity and structures. Once one cycle ends, the next one begins.

2. A Focus on One Thing — Foundational Learning — and Doing It Well

While the needs of children in the developing world are vast, they cannot all be effectively addressed simultaneously by one international nongovernmental organization. Focusing on what you do best allows you the time and capacity to refine your approach until you reach excellence. At Luminos, we do one thing: provide joyful, foundational learning to marginalized children. Our singular focus enables iteration, allowing us to home in on the adjustments and adaptations needed to achieve maximum impact for our students.

3. Consistent Classroom-Level Implementation

In pursuit of foundational learning and in support of our community teachers, Luminos applies a structured pedagogical approach to our curriculum. Structured pedagogy involves breaking down complex concepts into smaller, manageable units and presenting them in a logical sequence in order to progressively build upon a child’s foundational knowledge. For example, when teaching students to read, we begin our phonics-based approach by ensuring students can identify letters, then the letter sounds, before blending those sounds into words of increasingly greater complexity, eventually progressing to reading individual words and then sentences.

This framework makes it easy for us to track how consistently our curriculum is implemented across classrooms, and whether individual students or whole classrooms are on track with set learning targets. By laying out clear expectations for children’s learning, our structured pedagogy, combined with our classroom observations and other data collection, allows us to know immediately if we are meeting our learning targets or not, and make adjustments accordingly.

4. Data Collection and Analytics

The ability to quickly and accurately collect data, and then process and learn from that data, is crucial to making adaptations. Across all Luminos’ program sites, we collect data through classroom observations made by supervisors and Luminos staff, student assessments, and external program evaluations. This data provides a clear picture of what is and is not working, and it enables us to focus our adjustments accordingly.

5. A Staff Committed to Excellence, and a Staffing Structure to Match

Iterative design is foundational to Luminos and is reflected in our Beliefs and Values. Among other things, staff commit to using research, data, and classroom observations in the tenacious pursuit of excellence to learn what works and take the initiative to problem solve and adjust our programming accordingly.

6. Extensive Communication and Consensus Building with Partners

From start to finish, Luminos works hand in hand with our community partners and government stakeholders to ensure the successful delivery of our programs. An iterative approach is often new for community and government partners. Sharing data on actual student learning levels and inviting collaboration on solutions is critical for bringing partners along on the iterative design journey.

Looking to the Future

While iterative design is a well-known model in other industries, it is rarely practiced among global education reformers. In a world in which 90% of children in low-income countries have not learned to read by age 10, effective interventions are essential to addressing the problem. We believe the way to get to those effective education interventions is by employing an iterative design approach. Education reform through iterative design is a hard journey, but our results in the classroom tell us that it is the only one worth pursuing.

Learning more in the Iterative Design element of the Luminos Method!

 

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