Assent vs. Consent (in Research)

In human subjects research, assent, consent, and parental permission are three distinct concepts that are easy to conflate but govern different people and different legal acts. Informed consent is the legally operative agreement given by someone with the authority to agree on their own behalf — an adult research subject. For a child, that authorizing act is parental permission (what 45 CFR 46 Subpart D calls permission rather than consent), given by a parent or guardian. Assent is the child’s own affirmative agreement to participate, sought in addition to that permission whenever the reviewing Institutional Review Board (IRB) determines the child is developmentally capable of providing it. None of the three substitutes for another.

Where the Requirement Comes From

The assent requirement is set out in the Common Rule at 45 CFR 46 Subpart D, “Additional Protections for Children Involved as Subjects in Research.” Section 46.402(b) supplies the operative definition: assent means a child’s affirmative agreement to participate in research, and mere failure to object, absent affirmative agreement, may not be construed as assent. Section 46.408 sets the full procedural structure: paragraph (a) covers soliciting and, where appropriate, waiving assent; paragraph (b) covers soliciting parental/guardian permission (including when one parent’s permission is sufficient versus when both parents must agree); paragraph (c) covers waiver of the permission requirement itself for specific protocol/population circumstances; paragraph (d) requires permission to be documented consistent with 45 CFR 46.117; and paragraph (e) leaves the manner of documenting assent, once required, to the IRB’s determination.

Why Assent Exists Alongside Parental Permission

Parental or guardian permission establishes that enrolling the child is legally and ethically authorized. It does not, by itself, establish that the child understands or is willing to take part. Assent addresses that second question directly: it treats the child as a participant with a voice in the decision, proportionate to their developmental capacity, rather than as someone research is simply done to once a parent has signed. Neither element substitutes for the other — both are independently required unless the IRB specifically waives one under the regulatory conditions that permit a waiver.

Assent vs. Consent vs. Parental Permission: The Three-Way Distinction

This is the comparison researchers actually search for, and the terms map to three different people and three different regulatory hooks:

• Consent — the legally authorizing act given by an adult, competent research subject on their own behalf, under 45 CFR 46.116.
• Parental permission — the legally authorizing act given by a parent or guardian on a minor’s behalf, under 45 CFR 46.408(b). It is functionally analogous to consent but is a separately defined term because a minor cannot give legally operative consent.
• Assent — the minor’s own affirmative agreement, under 45 CFR 46.402(b)/46.408(a), required in addition to — never instead of — parental permission whenever the IRB finds the child capable of providing it. Assent is not legally authorizing on its own; a child who assents but whose parent withholds permission still cannot be enrolled.

A fuller side-by-side treatment, including when assent can be waived, is available on CASRAI’s Informed Consent vs. Assent comparison.

Age and Capacity Thresholds: Why There Is No Single Federal Age

Subpart D deliberately does not set a fixed age at which assent becomes required. 45 CFR 46.408(a) instead directs the IRB to determine capability by taking into account “the ages, maturity, and psychological state of the children involved,” and permits that judgment to be made either for an entire protocol’s pediatric population or on a child-by-child basis, as the IRB deems appropriate. In practice this means the same protocol can call for a formal written assent process for a 16-year-old cohort and a simplified verbal script, or no assent solicitation at all, for a study enrolling toddlers who cannot meaningfully understand what is being asked of them. Individual institutions commonly publish their own internal guidance on typical age bands (for example, treating assent as generally solicitable from around age 7 upward, with a written signed form more common from early adolescence on), but those thresholds are institutional practice, not a federal regulatory requirement — the actual legal standard is the case-by-case capability determination in 46.408(a).

How IRBs Determine Whether — and How — Assent Applies

Because the capability determination is IRB-specific rather than age-specific, the same underlying regulatory language does double duty for both the threshold question (is assent required at all) and the format question (how should it be solicited and documented). IRBs also determine the manner assent is documented — which can range from a signed, age-appropriate assent form mirroring the adult consent document, to a brief spoken explanation with a documented verbal agreement, depending on the study’s risk level and the subjects’ capacity.

When Assent May Be Waived

45 CFR 46.408(a) recognizes distinct routes by which assent is not required, or may be waived, even where the IRB might otherwise expect to solicit it:

• The children are not capable of assenting. If the IRB determines that the capability of some or all of the children involved is so limited that they cannot reasonably be consulted, assent is not a necessary condition for proceeding.
• Direct benefit available only in the research context. If the intervention or procedure holds out a prospect of direct benefit that is important to the child’s health or well-being and is available only in the research context, assent is likewise not a necessary condition — even for children who would otherwise be capable of providing it.
• General waiver under the consent-waiver conditions. Even where children are capable of assenting, the IRB may still waive the assent requirement under the same circumstances in which consent could be waived under 45 CFR 46.116 (the standard minimal-risk waiver-of-consent criteria) — see CASRAI’s waiver of informed consent guide and the 46.116(f) waiver term for that underlying test.

Separately, 46.408(c) allows the IRB to waive the parental permission requirement itself — not assent — for research designed for populations where parental permission is not a reasonable protection (for example, research involving neglected or abused children), provided an appropriate alternative protection mechanism is substituted and the waiver is consistent with applicable law. That is a waiver of permission, distinct from a waiver of assent, and the two should not be conflated when documenting an IRB determination.

Documentation of Assent

Unlike parental permission, which 46.408(d) requires to be documented consistent with the informed-consent documentation rules at 45 CFR 46.117, the regulation does not prescribe a fixed documentation method for assent itself. Under 46.408(e), once the IRB determines that assent is required, it also determines whether and how that assent must be documented. Institutional practice ranges from a signed, age-appropriate written assent form (often mirroring the structure of the adult consent form but written at a simpler reading level) to a documented verbal assent process for younger children or lower-risk studies, with the study team noting in the record that assent was sought and obtained.

Drafting an Age-Appropriate Assent Form

Because the regulation leaves format to IRB discretion, the practical drafting task is to match the document to the child’s actual comprehension level rather than reusing adult consent language at a smaller font size. Considerations that commonly shape an assent form:

• Reading level and vocabulary appropriate to the age band the study enrolls — many IRBs expect distinct forms for, e.g., young children versus adolescents, rather than one document for the full pediatric range.
• Plain description of what will happen to the child in the study, in concrete, first-person-relatable terms rather than clinical/legal phrasing.
• An affirmative response mechanism — a signature line, a verbal “yes” script with documentation, or an equivalent — since 46.402(b) specifically excludes passive non-objection from counting as assent.
• Consistency with the parental permission document on what the study involves, so the two documents describe the same procedures without contradicting each other.
• Review by the IRB as part of the same submission that includes the parental permission/consent document — assent language is not typically reviewed on a separate track.

See CASRAI’s informed consent checklist for researchers for the parallel checklist on the adult/parental-permission side of the same submission.

Related CASRAI Resources

• Informed consent — the general operational definition and requirements under the Common Rule.
• 45 CFR 46 Subpart D (Additional Protections for Children in Research) — the full regulatory structure governing pediatric research risk categories and permission/assent requirements.
• Vulnerable Populations in Research
• IRB (Institutional Review Board)
• Common Rule (45 CFR 46)
• Waiver of informed consent (45 CFR 46.116(f))
• Waiver of informed consent (guide)
• Informed Consent vs. Assent — comparison