Nonaccidental physical injuries children suffer at the hands of their parents occur along a continuum that ranges from mild to severe. At the outer edges of this continuum, one might find, on the one hand, a slight swat to the buttocks, and on the other, a brutal beating. In the United States, the normative consensus appears to be that outsiders to the family are appropriately concerned only when the physical injury at issue causes serious harm; any injury short of a serious one is exclusively “family business.”Consistent with this consensus, all states’ laws permit the use of “reasonable” corporal punishment; simultaneously, they all prohibit non accidentally inflicted serious injury. The latter is generally denominated abuse, although some states classify milder but still impermissible injuries as neglect, or simply “inappropriate discipline.” Thus, being able to distinguish between reasonable corporal punishment and maltreatment—whether this is formally denominated abuse or neglect—is critical for the relevant actors: parents who use corporal punishment as a disciplinary tool, child protective services (CPS) staff who are required by statute to intervene in the family to protect children subject to or at risk of abuse, and courts adjudicating issues arising in connection with these cases. The integrity of the distinction and of the methodology employed to make it is also critical for a society that is prominently committed to both family autonomy and child welfare, and in particular to protecting the integrity of the family when it promotes (or at least does not harm) child welfare, and to intervening in the family when it fails in its related obligations.Unfortunately, few if any states have sufficiently defined the relevant terms “reasonable corporal punishment” or “maltreatment” (abuse or neglect) to consistently guide the relevant actors (those in a single system) in their exercises of discretion; nor have they established a coherent methodology for sorting injuries along the continuum of nonaccidental physical injuries. That administrative regulations and policies promulgated by state and local CPS departments often narrow agency discretion helps CPS itself to be more consistent and may help families know what to expect when they are dealing with CPS. But because appellate courts do not appear to give much deference to agency interpretations of the statutory definitions, these regulations and policies do little to guide the courts’ own exercise of discretion. Moreover, to the extent that the law in statutes and judicial opinions is either less precise or even different from the law as it is applied by CPS, the public and parents are inevitably confused or misled. As a result, decisionmaking about whether an injury or incident remains in the realm of family business or has crossed the line into the impermissible varies, reflecting a multiplicity of purely personal viewpoints, religious and political ideologies, and academic or disciplinary training and requirements. In turn, institutional treatment of and outcomes for children and families are often inconsistent. The status quo has been defended or at least explained on several grounds. The vagueness of abuse definitions has been consistently upheld on policy grounds—specifically on the argument that it is important for authorities to retain flexibility to call injuries as they see them given that, particularly in a diverse society, abuse might appear in unexpected forms.