Why More Revision Often Leads to Lower Grades

The Productivity Paradox: When Studying Longer Stops Helping

Many parents believe that if their child isn’t doing well, the solution is simple: more revision... More worksheets. More hours at the desk. More homework after dinner.

But what if studying longer is actually reducing efficiency, and sometimes even hurting results?

In 2025, researchers from the University of Oviedo in Spain studied the academic performance of 7,725 students, analysing how their daily revision time affected outcomes.

The findings revealed something surprising.

The 70-Minute Threshold

The study found that the average effective revision duration was about 70 minutes per day.

Students who studied within that range generally saw improvements.

However, once students began studying between 70–90 minutes daily, the gains started to decline.

In fact, researchers noted that:

“That small gain requires two hours more homework per week, which is a large time investment for such small gains.”— Javier Suárez-Álvarez, co-lead author

In other words, the return on time invested began to shrink significantly.

More time did not mean proportionally better results.

So Is 70 Minutes the Magic Number?

Not exactly.

Because revision efficiency doesn’t just depend on total time — it depends on how long a child can sustain deep focus.

Child psychologists suggest that a reasonable attention span is approximately 2–3 minutes per year of age.

For example:

• An 11-year-old (P5 student) may sustain around 22–33 minutes of deep focus before needing a reset.

Beyond that, the brain’s efficiency naturally declines.

So instead of one long 70-minute block, structured shorter sessions may be more effective.

The Science of Brain Energy: Ultradian Cycles

There’s also a biological reason behind this.

American physiologist and sleep researcher Nathaniel Kleitman discovered that our bodies operate in ultradian cycles — natural rhythms that govern energy and alertness throughout the day.

These cycles suggest that after sustained mental effort (often around 60–90 minutes for adults, shorter for children), the brain requires a recovery period.

Ignoring these rhythms can lead to:

• Mental fatigue

• Reduced retention

• Increased frustration

• Lower-quality revision

In short, pushing through exhaustion doesn’t build resilience — it reduces performance.

What Actually Improves Results?

According to the University of Oviedo researchers:

“It is not necessary to assign huge quantities of homework, but it is important that assignment is systematic and regular, with the aim of instilling work habits and promoting autonomous, self-regulated learning.”

This means:

• Consistency beats cramming

• Structure beats volume

• Quality beats quantity

Students benefit more from clear systems, regular practice, and healthy study habits than from marathon revision sessions.

What This Means for Parents

If your child is studying longer but not improving, the issue may not be effort — it may be efficiency.

Instead of asking:“How many hours did you study?”

Consider asking:

• Was the session structured?

• Were breaks intentional?

• Was the workload realistic?

• Did they review systematically?

The goal is not to maximise hours.

The goal is to maximise retention, confidence, and long-term learning habits.

Because sometimes, the smartest way to improve grades… is to study less — but better.

At Overmugged, we don’t just teach students what to learn, but how to learn. By shifting the environment from high-pressure to high-efficiency, we help students reclaim their confidence and parents reclaim their evenings.