Toilet training generates comparison and anxiety, and the variation between children who develop entirely normally is very wide.
What has to develop
Physical control of the relevant muscles, which develops over a period.
Awareness of the sensation before rather than after.
The ability to communicate it.
Motor skills to manage clothing and get to the toilet.
And willingness, which is not a physical capacity and is frequently the limiting factor.
Readiness signs
Guidance generally lists indicators including staying dry for longer periods, showing awareness of elimination, interest in the toilet, discomfort with soiled nappies, and ability to follow simple instructions.
Which are indicators rather than requirements, and children show them at widely varying ages.
Starting before readiness generally extends the process rather than accelerating it, which several studies have found.
Cultural variation
Age at training varies enormously between countries and has shifted historically within them.
Which reflects practice rather than biology — in societies where training begins in infancy through timed positioning, children are out of nappies far earlier.
The introduction of disposable nappies is associated with later training ages across several countries.
Which means the current typical age in any country is a convention rather than a developmental fact.
Approaches
Child-oriented approaches wait for readiness signs and proceed at the child's pace.
Structured intensive approaches use a concentrated period with frequent prompting and reward.
Timed approaches place the child at intervals regardless of signals.
Evidence comparing them is limited, and reviews find insufficient evidence to strongly recommend one over another for typically developing children.
What tends to help
Consistency between caregivers and settings.
Positive rather than negative attention, since pressure and punishment are associated with prolonged difficulty.
Clothing the child can manage.
Access and familiarity with the toilet or potty before starting.
And avoiding starting during other significant changes — a new sibling, moving house, starting nursery.
Regression
Common and generally temporary, frequently associated with change or stress.
Which is expected rather than a failure, and returning to a lower-pressure approach generally resolves it.
Night dryness
Develops separately and considerably later than daytime control.
Which depends on hormonal development and on arousal from sleep, neither of which is under voluntary control.
Bedwetting is common at ages when parents frequently expect it to have stopped, and it is not a behavioural problem.
Guidance generally suggests it warrants assessment beyond a certain age, and effective treatments exist including alarms and medication.
When to seek advice
Pain or difficulty passing urine or stool.
Constipation, which is a very common underlying cause of difficulty and withholding.
Persistent daytime wetting beyond the expected age.
Regression that persists.
Or loss of previously established control.
Which should go to a health visitor or doctor, and treatable causes are common.
Constipation
Worth its own section because it is common and frequently missed.
Withholding stool causes it, it makes passing stool painful, and pain causes further withholding.
Which is a cycle that will not resolve through training approaches and requires treatment.
Signs include infrequent or hard stools, soiling, straining and abdominal pain, and a doctor should be consulted.
Nursery and school
Settings have varying policies on toilet training, and legal positions on requiring it differ by jurisdiction.
Which is worth clarifying in advance, and children with additional needs have protections in many places.
Additional needs
Children with developmental differences frequently train later, and specific approaches exist.
Which is supported by specialist services, and pressure to meet typical timelines is unhelpful.
Practical setup
A potty or a seat with a step, since dangling feet make it harder to push.
Clothing that a child can manage independently.
Consistent language between caregivers.
And accepting accidents without reaction, since a reaction adds pressure to something that is already effortful.
Rewards
Small immediate acknowledgement works better than elaborate reward systems, which become difficult to withdraw.
Which is consistent with the general finding about external rewards.
Out and about
Public toilet access is a genuine practical constraint, and knowing where facilities are reduces the pressure on both parties.
Portable potties and spare clothing address most of the difficulty during the transition period.
Timing
Warmer months are frequently suggested for practical reasons, and there is no developmental basis for it.
Comparison
The range of normal is wide enough that comparison with other children produces anxiety without information.
Which is worth remembering during a period when it is discussed constantly among parents of similar-aged children.
Second and subsequent children
Frequently train earlier, which is attributed to observation of older siblings and to parental confidence rather than to anything about the child.
Which means comparison within a family is as unreliable as comparison between families.
The long view
Essentially all children achieve this, and the age at which they did becomes irrelevant very quickly.
Which is worth holding onto during a period that feels significant and is not.