Why Some Children Can Cope One Day And "Fall Apart" The Next

One of the most confusing experiences for people working in education, care, and therapeutic settings is watching someone cope well one day and then struggle profoundly the next. It can be disorienting. One day a child engages, participates, follows instructions, and meets demands that once felt impossible. There is relief in the room. Professionals feel reassured that progress is being made. Families begin to relax and rebuild confidence. Then, often without warning, everything changes. The same child who seemed settled and capable may now be withdrawn, irritable, or completely overwhelmed by something that appears trivial. From the outside, it looks like inconsistency. From the inside, it is the nervous system doing its best to survive.

I have come to believe that what changes in these moments is not motivation or character. It is not willpower, stubbornness, or mood. What changes is capacity. When I talk about capacity, I am not referring to intelligence or long-term ability. I am talking about the moment-to-moment ability to access those abilities under particular conditions. Capacity is dynamic. It fluctuates depending on what the nervous system is carrying at that time. Stress, fatigue, hunger, emotional load, sensory stimulation, predictability, relational safety, and physical wellbeing all contribute to it. Capacity is not something we either have or do not have. It is something that shifts and reshapes itself in response to context.

Once we begin to view behaviour through this lens, what appears inconsistent becomes coherent. Behaviour is never random. It is communication expressed through physiology. The human nervous system is constantly assessing for safety, risk, and predictability. It does this outside conscious awareness. It is shaped by memory, experience, and anticipation. It responds to what has happened, what is happening now, and what it expects may happen next. When the nervous system perceives safety, we are able to think, reflect, learn, and connect. When it perceives threat or instability, those higher cognitive processes become less available. The difference between coping and collapsing is often not skill but access.

In systems that value consistency, this can be difficult to accept. Once a person has demonstrated that they can complete a task or follow a routine, we tend to assume that ability should remain available at all times. A child who reads fluently one day is expected to do so again the next. An adult who communicates clearly on a good day is assumed to have no reason not to do so on a bad one. Expectations are set according to best-day performance, as though success represents a permanent upgrade. When capacity fluctuates, it is often viewed as regression or non-compliance rather than a reflection of stress, depletion, or overload.

For me, this misunderstanding sits at the heart of many challenges in behaviour support. We confuse knowledge with access. We assume that because someone can do something, they should always be able to do it. But human beings do not operate that way. Access to skill is state-dependent. It is filtered through the nervous system’s capacity at that moment. A person may know exactly what they should do, yet be unable to organise their body and attention to do it. The nervous system prioritises survival, not performance. When energy is diverted toward protection, reasoning and learning are the first functions to fade.

This explains why good days and bad days are not simply random fluctuations. They are the visible outcomes of invisible load. On a good day, the person’s body and environment are working together. There is rest, predictability, and relational safety. On those days, capacity expands and engagement becomes possible. On a more difficult day, the person may arrive already carrying stress, fatigue, sensory overload, or unprocessed emotion. The same demand now draws on a system that is already taxed. It is not the demand that has changed, but the weight of what must be carried alongside it.

The idea of cumulative load helps to make sense of this. The nervous system does not reset overnight. Effort accumulates. Masking accumulates. Stress accumulates. A person may appear composed for days or weeks, holding everything together, until one day that capacity quietly gives way. From the outside, this can look like sudden escalation or unexplained distress. From the inside, it is the predictable outcome of prolonged effort. The body has reached its threshold. What is often described as “a meltdown out of nowhere” is rarely out of nowhere at all. It is the nervous system’s way of releasing pressure that has been building invisibly.

This pattern is not confined to children. Adults experience it too. The employee who meets every deadline and then suddenly burns out. The parent who keeps everything together until one minor thing tips them over the edge. The practitioner who supports others with compassion but finds their own patience running thin. We are all subject to the same physiological principles. The body can only sustain effort for so long without repair. When recovery is insufficient, even familiar demands become heavy.

Anticipation also shapes capacity in powerful ways. The nervous system is predictive. It prepares for what it expects to come. A child may become tense or withdrawn hours before a known event. An adult may feel drained in advance of a difficult meeting. Sometimes what looks like avoidance is actually the body bracing for what it perceives as a threat. The brain is not responding to what is happening now, but to what it believes is imminent. This is why people sometimes appear to struggle “too early” or “for no reason.” Their nervous system is already preparing to protect them.

Despite these realities, behaviour is still too often interpreted through a narrow behavioural lens. Someone who cannot meet an expectation is described as inconsistent, unmotivated, or unwilling. These descriptions reflect the perspective of the observer, not the reality of the person. They tell us that the adult values consistency and control, not that the child lacks effort. This kind of framing is seductive because it preserves our sense of order. It implies that if we apply the right strategy or consequence, behaviour will become predictable again. But human beings do not thrive in systems built on control. They thrive in systems built on understanding.

For individuals who are neurodivergent or who have limited expressive communication, this misunderstanding can be even more pronounced. Many cannot use spoken language to describe when something feels too hard or when their capacity is reducing. Their behaviour becomes their primary form of communication. A subtle change in tone, movement, or engagement might be an early signal that the nervous system is struggling. When adults focus only on verbal cues, these messages go unnoticed until they are expressed more loudly. Escalation, then, is not sudden. It is the result of communication that has gone unheard.

This is why observation and attunement matter as much as strategy. The practitioner who notices that a child’s shoulders have tensed, that their voice has changed, or that their responses are slower than usual is witnessing the earliest signs of strain. Responding at this point can prevent crisis later. Reducing demands, slowing the pace, or offering reassurance at the right time can preserve capacity and prevent escalation. It is not permissive practice. It is responsive practice. It recognises that safety, not compliance, is the foundation of all regulation.

Sensory processing differences add another dimension to this. Many people experience what I think of as sensory debt. Sensory input accumulates like emotional or cognitive effort. Noise, light, touch, and movement that are tolerable at one point in the day can become overwhelming later as resources deplete. This explains why some children cope well at school but fall apart at home, or manage structured environments but struggle in unstructured ones. Their systems have used up available regulatory resources. Behaviour reflects not only the present sensory experience but also the cumulative load that has built over time.

Physical health can be just as influential. Pain, illness, hormonal fluctuations, hunger, or fatigue all alter capacity. For individuals who cannot easily recognise or communicate discomfort, behaviour often becomes the first clue that something is wrong. I have seen children described as oppositional who were later found to be unwell, or adults labelled as unmotivated who were simply exhausted. When behaviour changes, it is always worth asking what is happening in the body as well as in the mind.

Predictability and control are equally important. Human beings need to feel that their environment makes sense. When routines change without warning or when people feel powerless, the nervous system interprets this as threat. Capacity drops sharply. What appears to be resistance is often an attempt to restore predictability. Similarly, relational dynamics shape capacity more than most people realise. The emotional tone, pace, and presence of those nearby influence how safe a space feels. Calmness in one person can help settle another. Frustration and urgency can amplify distress. Regulation is relational. We affect each other constantly.

When we take all of this together, behaviour stops appearing unpredictable. It becomes logical. It is the visible expression of a nervous system in context, interacting with environment, relationship, and history. What we call inconsistency is the natural rhythm of human adaptation. The nervous system is dynamic by design. It contracts and expands according to what it senses.

Recognising this does not mean removing all expectations or boundaries. It means matching them to capacity. It means understanding that growth happens at the edges of tolerance, not beyond them. When expectations consistently exceed capacity, behaviour is not a possibility. It is a certainty. The nervous system will respond in whatever way it needs to preserve safety, even if that response is misunderstood.

This reframing also invites us to consider how our systems contribute to the very patterns we find challenging. Educational, healthcare, and social care environments often prioritise performance, efficiency, and compliance. These values leave little space for noticing when someone begins to falter. They reward perseverance and penalise rest. Over time, this creates conditions where masking is celebrated and distress is hidden. The individual learns that safety depends on silence and success. The cost of this is enormous.

When we begin to see behaviour as communication rather than defiance, the role of the adult changes. We become interpreters, not enforcers. Our task shifts from managing behaviour to understanding capacity. Instead of asking “What is wrong with you?” we begin to ask “What is happening for you?” and “What might your nervous system be trying to tell me?” These questions open the door to empathy and flexibility. They require us to slow down, to think critically about our own responses, and to reflect on whether the environments we create support or constrain capacity.

For me, this understanding has shaped every aspect of my work. It reminds me that people are not inconsistent. They are responsive. They are navigating the world with the resources available to them. It reminds me that my own regulation matters just as much as anyone else’s, because how I show up affects the capacity of those around me. It also reminds me that meaningful support requires curiosity, not certainty. When I approach behaviour with humility, I learn more.

If you are supporting someone who seems to cope one day and struggle the next, I would encourage you to pause before labelling it as unpredictable. Ask instead what has changed in their environment, their body, or their relationships. Consider what has accumulated and what they may be anticipating. Think about how predictable the world feels to them and whether they have enough capacity left to meet the demand being placed upon them.

People are not unreliable. Nervous systems are dynamic. They respond to safety, context, and connection. When we understand this, we stop expecting people to function like machines and start supporting them as human beings.

If this reflection resonates with you, I welcome your thoughts, comments, or experiences. SENteachCo is intended to be a reflective space for exploring complexity and thinking deeply about how we understand behaviour. Your insights, perspectives, and stories are an important part of that conversation.