A reform school in the United States was a term used to define, often somewhat euphemistically, what was often essentially a penal institution for boys, generally teenagers.

Social reformers in America in the late 19th and early 20th centuries almost invariably found fault with the then-usual practice of treating juvenile offenders essentially the same as adult criminals. It was recognized that the juveniles were often sexually and otherwise exploited by the older inmates and that they were often receiving instruction in more advanced and hardened ways of crime by hardened criminals with little regard for law, society's mores, or even human life. As a result, rather than their sentences serving as a deterrent to future crimes, many juvenile offenders emerged from incarceration far worse than when they were first sentenced.

The reforms, which were adopted far more readily in some states than others, consisted of a two-pronged apporach, a separate juvenile code and juvenile courts for offenders who had not reached the age of majority, and the building of separate institutions for juvenile "delinquents" (the stigmatizing term "criminal" not being used). Because the primary purpose of these institutions was to be rehabilitative rather than punitive, they were styled "reform schools". For the most part, these institutions were custodial.

In the 1950s and 1960s, many of the same problems that had occurred with the former system of incarcerating juveniles along with adults began to be noticed in reform school -- older juveniles exploiting the younger ones, sexually and otherwise, and the younger ones taking the more hardened, usually older offenders, as role models and mentors. Also, the term "reform school" itself, originally intended as destigmatizing, had developed its own stigma, much as the way "welfare payments" were intended to be the destigmatizing corrective term for "relief" or "the dole", but developed a stigma of its on.

Today, no state openly or officially refers to its juvenile correctional institutions as "reform schools", although such institutions still exist. The attempt has also been made to reduce the population of such institutions to the maximum extent possible, and to leave all but the most incorregible youths in a home setting. Also, in an attempt to make the situation more socially normal, and in response to the rising number of young female offenders, many such institutions have been made coeducational.

The current approach involves minimizing the use of custodial instiutions and the maximization of the use of less-restrictive settings which allow the youths to remain in their own homes, usually while attending during the daytime an institution called an "alternative school" or something similar, which is usually a more-structured version of a public school. There may be court-monitored probation or other restrictions, such as a stricted curfew applied to the clientelle of the "Department of Youth Services" or whatever the state terms it, than for other youths the same age.

In the United States, the most well-known facilities meeting the general criteria for being coloquially labelled "reform schools" include the Lincoln Hills School near Merrill, Wisconsin (mentioned in episodes of the once-popular TV series Picket Fences) and the Preston School of Industry in Ione, California.