Evidence Based Teacher Development Starts With an Uncomfortable Truth
Why evidence-based strategies fail when the conditions for success are ignored
Evidence Based Teacher Development exists because evidence alone is not enough.
Evidence-based strategies only work when the conditions that make them effective are in place — and too often, teachers are asked to apply them without that support.
That sentence may already feel familiar. If you’ve ever tried to implement a “best bet” strategy in a class of 40 students, five minutes before lunch, you’ll know exactly why. In theory, everything lines up perfectly. In practice, the bell goes, the seating plan hasn’t loaded, and at least one student is still convinced this lesson is about something else entirely.
This isn’t a gripe. It’s a research-backed reality.
A recent peer-reviewed study by Redifer et al., published in Instructional Science, tested one of the most widely promoted evidence-based strategies in education: retrieval practice. But unlike most laboratory research, this study did something unusual. It used complex, authentic academic material — a full research article — rather than short passages or neatly packaged facts.
The result?
Retrieval practice did not improve learning outcomes.
Before anyone panics and throws their mini-whiteboards out of the window: this wasn’t because retrieval practice “doesn’t work”. It was because cognitive load overwhelmed the learner.
And that distinction matters far more than most CPD sessions ever acknowledge.
When “evidence-based” becomes dangerously tidy
The evidence-informed movement has done teaching a huge service. It has challenged tradition, raised expectations, and helped many teachers stop doing things simply because “that’s how it’s always been done”.
But somewhere along the way, something odd happened.
Evidence became neat.
Strategies became portable.
Complexity quietly disappeared.
Suddenly, teaching improvement sounded like this:
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“Just use retrieval practice.”
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“Add desirable difficulties.”
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“Make learning harder.”
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“Quiz more.”
Simple. Clean. Reassuring.
Except teaching has never been any of those things.
No one teaches in a laboratory. Teachers teach in classrooms where:
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students forget what you said thirty seconds ago
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the projector doesn’t work
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half the class is still decoding the question
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one student is staring out of the window as if contemplating the meaning of life
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another appears to be on a completely different planet
And yet we act surprised when a strategy that works beautifully under controlled conditions delivers mixed results on a wet Tuesday afternoon in period five.
What the research actually shows (and why it’s oddly reassuring)
In the Redifer et al. study, participants either reread the material or used different forms of retrieval practice. One week later, all groups completed a final assessment.
There was no advantage for retrieval practice.
But the researchers didn’t stop at “it didn’t work”. They asked why.
Their analysis showed that retrieval practice:
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significantly increased cognitive load
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and that this cognitive load fully mediated performance outcomes
Once mental effort was accounted for, the strategy itself no longer predicted learning. Students who experienced higher cognitive demand during strategy use performed worse later — regardless of which strategy they had been assigned.
The effort was real.
The strategy was evidence-based.
But the brain was already busy doing something else.
Teachers recognise this instantly. It’s the moment when you ask a perfectly reasonable question and are met with that familiar pause — the one where students are clearly working very hard, just not on the thing you hoped.
When effort stops being helpful (and starts being exhausting)
Retrieval practice is often justified through the idea of desirable difficulty: learning should feel effortful because effort strengthens memory.
True.
But effort is not magic. It is not unlimited. And it is not always helpful.
Cognitive Load Theory reminds us that working memory has limits. When learners are still grappling with understanding — building mental models, decoding language, making sense of ideas — adding an extra demand does not deepen learning. It competes with it.
The Redifer study shows this clearly. Retrieval practice layered onto already complex material pushed learners beyond the point where effort was productive. Difficulty stopped being desirable and became, quite simply, difficult.
We’ve all seen that look in students’ eyes. The one that says they are trying, but there is very little capacity left to draw on.
The real problem isn’t teachers
At Evidence Based Teacher Development, we work with teachers who care deeply about their craft. They read research. They attend training. They try to improve.
They are not failing to implement evidence-based strategies.
They are being asked to implement them without the conditions that make them effective.
When results disappoint, the response is often:
“Be more consistent.”
“Do it more often.”
“Stick with it.”
At this point, teaching advice can start to resemble troubleshooting a faulty speaker: turning it up louder doesn’t fix the problem — it just makes the distortion harder to ignore.
Sometimes the problem isn’t commitment.
Sometimes it’s load.
Sometimes the most evidence-based thing a teacher can do is not add another strategy, but remove pressure, slow the sequence, or give students time to understand before asking them to retrieve.
That takes judgement. And judgement is not something you get from a checklist.
Why this matters in real classrooms
The conditions that caused retrieval practice to falter in this study are not rare. They are everyday teaching conditions:
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dense curricula
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large classes
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language and literacy demands
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assessment pressure
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limited time
In Bangladesh and many other education systems globally, cognitive load is not a theoretical concern. It is a daily reality.
Evidence-based teaching that ignores this reality risks becoming performative — something teachers are seen to do, rather than something that genuinely helps students learn.
What genuine evidence-based teacher development looks like
If we take the research seriously — and we should — then evidence-based teacher development must include:
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attention to when strategies are used, not just which ones
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curriculum thinking that distinguishes encoding, consolidation, and transfer
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recognition that not all knowledge is equally retrievable
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professional learning that builds teacher judgement, not just technique compliance
This is harder than handing out strategies.
But it is also kinder.
Kinder to teachers.
Kinder to students.
And far more honest.
Why Evidence Based Teacher Development exists
The Redifer et al. study doesn’t undermine evidence-based education. It strengthens it — by reminding us that evidence has limits, conditions, and consequences.
If we really want better outcomes, we need to stop asking “What works?” in isolation.
And start asking the questions Evidence Based Teacher Development was built around:
What works for these students?
What works in this context?
What works after what came before?
What works on a normal Tuesday, when the projector is “warming up”, the Wi-Fi is “thinking about it”, and someone has asked if this will be on the test before you’ve even finished the sentence?
That’s not a gimmick.
That’s the work.
Reference
Redifer, J. L., Myers, S. J., Bae, C. L., & Scott, A. (2026). Testing the testing effect with advanced materials while accounting for individual differences. Instructional Science. https://doi.org/10.1007/s11251-025-09758-z
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