Effective Lesson Planning: length of lessons

Some of the questions, concerns and issues raised by trainee teachers so far include:

  • constantly repeating instructions to students
  • students forget what to do
  • students either don’t finish the tasks in the time set or finish in the first 5 minutes with nothing else to do

What these questions raise for me is an understanding of why we plan lessons in the way we do. So I thought some shared understandings about lesson planning here would be useful.

The length of lessons can vary greatly from 20 minutes to 90 minutes.

Most teachers try to fit their lessons into a school timetable that is constructed for many different reasons e.g. when specialist subject lessons occur, compliance with industrial agreements on teacher breaks or administrative time and when support programs like reading recovery occur.  Timetables are not necessarily about when or how its best for students to learn.

The school instructional day is 300 minutes long in Victoria, something like 9.00 am- 11.00 am (then a 30 minute recess) 11.30 am – 1.00 pm (then a 60 minute lunch) and 2.00 pm till 3.30 pm.

So my first bit of advice for trainee teachers is yes you have to comply with a school timetable but don’t let that completely dominate the length of lessons you facilitate. Just because you have 120 minutes (first period) or 90 minutes (second or third periods) does not mean lessons have to be that whole period or even half that period (60 or 45 minute lessons). There are in fact well researched reasons why you vary the length of lessons from 20 to 45 minutes and perhaps even break lessons into smaller blocks .

There are a few key understandings I suggest trainee teachers take note of

  • David Sousa’s research on the brain and student retention, and
  • Ebbinghaus forgetting curve are two

David Sousa’s has written over 20 books on this topic of how the brain learns. One of his points for teachers is about student retention during lessons.

I have presented his work on primacy and recency retention in a typical 40 minute lesson as most lessons presented to students tend to be around this sort of length of time. The diagram illustrates there are two prime times for the retention of new information in a 40 minute lesson: prime time 1 where students remember new information and prime time 2 where near the end of the lesson we revise the key points for a recency effect.

If we were to make the lesson a 20 minute lesson lets look at the student retention blocks (prime times 1 and 2) and you can see the reduced amount of down time. That’s surely a positive.

Now if we combine two twenty-minute lessons together lets look at the effect.

As we can clearly see the amount of prime time 1 where new information is retained with prime time 2 for recency effects they are double that of a 40 minute lesson.

Now if you add Ebbinghaus Forgetting Curve into the argument for some short lessons that enable some repetition of new content over 2 or 3 days then the percentage of new information being retained by students is potentially increased.


So how does this answer some of the questions being posed above:

  • If you have shorter lessons then the chance that student forget your instruction (in downtime) is reduced.
  • If you give your instructions before students hit the downtime then there is a greater chance they will be remembered and thus cut constant teacher instructional repetitions.

There are other points to make here about how to structure a lesson be it 20 or 40 minutes and what learning tasks support retention but that will be the subject of my next post.

I hope that’s useful information and as always I welcome feedback.

Some useful links for further information are provided below: