Lead
A physician leans toward a school-age child before a procedure and asks: "We're going to do this test — are you okay with that?" The child nods.
What does that nod mean? The parent has already provided legal consent, so nothing about the medical act turns on the child's response. Why ask at all?
The answer is not ceremony. Asking is a practice of treating the child as a person — a participant in what is happening to their own body. Pediatric medical ethics has spent more than 30 years working out what that practice should look like.
What Assent Means
Medical consent, in its standard form, is something adults give autonomously. Children, legally, fall under the authority of their parents or guardians. The concept that fills the space between is assent: a child's voluntary agreement to a medical procedure, ethically distinct from legal consent, which remains with the parent or guardian — a child's affirmative agreement to a proposed medical intervention, understood as distinct from, and complementary to, the consent provided by the legal guardian.
The American Academy of Pediatrics (AAP) articulated the framework for assent in a 1995 policy statement [1]. Four elements were identified as components of meaningful assent in the context of informed consent: (1) explanation of the child's condition in age-appropriate terms; (2) assessment of what the child understands about their situation; (3) solicitation of the child's assent where they are capable of giving it; and (4) structuring of the process to involve both guardian and child [1].
The 2016 revised technical report extended and operationalized this framework [2]. Decision-making capacity, it notes, develops along developmental lines: partial capacity begins to emerge around age seven; by adolescence, many children possess reasoning abilities that approximate adult-level judgment in at least some domains [2]. Capacity is not a switch that flips at a particular birthday — it is a gradient, and the clinical task is to assess where a given child falls on it.
Gillick Competence: The UK Standard
A parallel and influential line of reasoning developed in the United Kingdom. The 1985 House of Lords decision in Gillick v West Norfolk and Wisbech Area Health Authority established that "a minor below the age of 16 could give valid consent to medical treatment provided that he or she has sufficient maturity and intelligence to understand the nature and implications of the proposed treatment" [3]. This standard — known as Gillick competence: the UK legal principle that a minor under 16 may consent to medical treatment if they sufficiently understand its nature and implications — locates the threshold not in age but in understanding.
The American and British frameworks differ in design and in the legal weight they assign to the child's response. In the Gillick framework, a sufficiently competent minor's consent can, in principle, be sufficient without parental consent; in the AAP framework, the child's assent and the guardian's consent operate in parallel. What the frameworks share is the underlying value: a child is not a passive recipient of medical care but a developing agent whose voice matters in proportion to their capacity.
The Empirical Research on Assent Capacity
What age and capacity thresholds does the empirical literature actually support?
Hein and colleagues conducted a prospective study in 2014 using the MacArthur Competence Assessment Tool for Clinical Research (MacCAT-CR): a structured interview measuring understanding, appreciation, reasoning, and choice to assess decision-making capacity with 161 participants aged 6–18 [4]. Assessing understanding, appreciation, reasoning, and expression of a choice — the four standard domains — they found that capacity, as measured by this instrument, showed a developmental inflection point around age 12, with scores below that age falling substantially lower than adult norms [4].
Miller, Drotar, and Kodish's 2004 review of the empirical evidence on children's competence for assent and consent traced the developmental trajectory in finer grain [5]. At ages six to seven, children's understanding is predominantly procedural: relating to the steps of what will physically happen, without necessarily grasping why or what risks are involved — they can grasp what will be done to them. From around age ten, teleological understanding: the ability to reason about the purpose and goals of a procedure, including its risks and potential benefits develops — they can engage with why a procedure is necessary and what its risks are. The quality of assent that can be meaningfully solicited shifts accordingly across these stages [5].
Wendler's 2006 theoretical analysis offered a clarifying move on the normative question: assent requirements should be reserved for children who have the capacity to give them meaningfully [6]. Soliciting formal assent from a very young child who cannot understand the relevant concepts does not honor the child's autonomy — it substitutes a procedural form for the thing itself. Assent, on this view, is not an obligatory checkbox. Its value lies in the dialogue it enables; that dialogue only functions when the child can participate in it [6].
The Context in Japan
In Japan, assent as a formal practice remains unevenly embedded in clinical settings. Informed consent structures have historically centered on the legal guardian, with child-directed explanation and the solicitation of the child's response treated, in many settings, as an optional courtesy rather than a procedural expectation.
That picture is shifting, at least in some domains. Ethics review of clinical research increasingly specifies child assent as a requirement. In pediatric oncology and other fields where treatment extends over years, clinicians have recognized that sustained therapeutic cooperation — adherence — is associated with the quality of the child's own relationship to the treatment, not only the guardian's authorization of it. A child who understands what is happening, and who has been genuinely asked, is more likely to remain an active participant in their own care.
The AAP's 2016 framework is worth keeping in mind as a practical reference even outside a US clinical context [2]. Its core claim — that age-appropriate explanation, followed by a genuine solicitation of the child's response, is clinically meaningful for children from roughly age seven upward — translates across healthcare systems. The specific procedural expectations differ by institution; the underlying developmental logic does not. Parents who understand the framework can ask for it by name, and can advocate for a clinical encounter that includes the child's perspective, regardless of what is standard practice at a given facility.
What Parents Can Do
When assent becomes relevant in a clinical encounter, there are things parents can do to support it beyond deferring to the physician.
Talking with your child before the visit — framing what will happen in accurate, age-appropriate language before you arrive — prepares the child to have their own voice in the room. "There will be a needle. It will hurt for a moment. Can you tell me how it feels afterward?" is not the same as "don't worry, it won't be a big deal." The first invites the child into their experience; the second closes the conversation before it begins.
When a child says "no" or "I don't want to," how that response is handled matters. Wendler is clear that a child's dissent does not always control the medical decision [6] — there are situations where a necessary procedure will proceed regardless. But having been asked, and having had their response received seriously, is itself an experience with developmental significance. A child who has learned that their voice is heard in medical settings carries that toward future interactions with healthcare as an adult.
If you are uncertain whether enough attention is being given to your child's understanding and response in a clinical encounter, saying so directly — "Can someone explain to my child what's about to happen?" — is a reasonable and useful thing to ask.
Summary
Assent is a practice of positioning the child as a participant in their own medical care rather than its object. Grounded in both developmental psychology and medical ethics [1,2,4], the practice asks for age-appropriate explanation, genuine dialogue, and attention to the child's response. Perfect understanding is not the threshold. The threshold is engagement — and the act of asking, of being willing to hear the answer, is already a recognition of the child's developing autonomy.
References
- Committee on Bioethics, American Academy of Pediatrics. Informed consent, parental permission, and assent in pediatric practice. Pediatrics. 1995;95(2):314–317. PMID: 7478854.
- Katz AL, Macauley RC, Mercurio MR, et al. Informed Consent in Decision-Making in Pediatric Practice. Pediatrics. 2016;138(2):e20161484. PMID: 27456514. doi:10.1542/peds.2016-1484
- Gillick v West Norfolk and Wisbech Area Health Authority [1986] AC 112. House of Lords (UK).
- Hein IM, Troost PW, Lindeboom R, et al. Accuracy of the MacArthur Competence Assessment Tool for Clinical Research (MacCAT-CR) for measuring children's competence to consent to clinical research. JAMA Pediatr. 2014;168(12):1147–1153. PMID: 25317644. doi:10.1001/jamapediatrics.2014.1694
- Miller VA, Drotar D, Kodish E. Children's competence for assent and consent: a review of empirical findings. Ethics Behav. 2004;14(3):255–295. PMID: 15875339.
- Wendler D. Assent in paediatric research: theoretical and practical considerations. J Med Ethics. 2006;32(4):229–234. PMID: 16574878. doi:10.1136/jme.2004.011114