The short answer
Thirty minutes, four days a week, beats an hour twice a week for almost every child. Reading is built by frequency, not by sitting longer, and a child who is tired for the last fifteen minutes of a long lesson is learning that the lesson is something to get through.
Why thirty minutes is the usual answer
A one-to-one lesson has no waiting in it. Nobody else is reading, nothing is being explained to the room, and the child is either reading aloud or being corrected for the whole half hour. That is far more concentrated than half an hour of a group class, and it is why thirty minutes here does the work of an hour somewhere else.
It is also the length a child can give full attention to at the end of a school day, which is when most of these lessons happen.
Four short lessons against two long ones
What we suggest
Four lessons of thirty minutes
- Two hours a week, spread outA gap of a day or two, never more.
- Mistakes corrected before they setA wrong sound is caught this week, not next.
- Each lesson starts where the last endedAlmost nothing is lost in between.
- A missed lesson costs littleOne day out of four, and the week still holds.
Two lessons of an hour
- The same two hours, in two sittingsIdentical on paper, slower in practice.
- Three or four days in betweenLong enough for a young child to forget.
- The first ten minutes go on rememberingPaid for, and spent recovering ground.
- A missed lesson costs half the weekAnd the next one starts further back still.
The hours are identical and the results are not. A child who reads four times a week forgets less between lessons, and the teacher spends the start of each one moving forward rather than recovering ground.
When a longer lesson is right
- Hifz. Memorising, revising the new portion and hearing old portions back does not fit in half an hour, and these lessons are longer for that reason.
- An older child who is reading fluently and wants to cover ground, and who asks for the longer lesson themselves.
- A family in a time zone where only one slot a day is possible, where length is buying back some of what frequency cannot give.
Outside those, a longer lesson is usually a parent buying reassurance rather than a child getting more reading.
How to tell the lesson is the wrong length
Too long
The last ten minutes go quiet, or the child starts asking how much is left. Shorten it before you change anything else.
Too short
The lesson ends mid-page every time and the child is still fresh. This is rarer than parents expect, and it usually means more days rather than longer ones.
Wrong hour, not wrong length
Flat at half past seven after homework, fine at half past four with a snack first. Try the hour before you touch the length.
What this means for the week
Pick the number of days first and the length second. Three or four days of thirty minutes is where most children sit, two days is the floor at which a child stops spending the start of each lesson remembering the last one, and five days suits a child working towards something with a date on it.