From the National Survey of Nonprofit Volunteer Screening Practices Criminal History
To determine whether a prospective Board member, volunteer or employee has a criminal record, the candidate's name and/or fingerprints are submitted to local, state, or national law enforcement, or to a state or national repository of criminal history record information (either government entities at the state level or private companies that collect and store information nationally).
Criminal records may include data on arrests or convictions. In general, name-based checks are faster and more convenient, but fingerprint-based checks are the most reliable, as they eliminate name mix-ups and the possibility of candidates using aliases to avoid detection of their criminal past.
Sex Offender Registry: All states currently have lists of registered sex offenders, many of which are available online. Organizations can search online sex offender registries, contact state or local law enforcement agencies or connect with private companies to learn whether a candidate is a registered sex offender in a given state.
Child Protective Services and Adult Protective Services: All states have designated entities responsible for the protection of children and vulnerable adults, and these entities (whose official names vary by state) keep records of reports of abuse, investigations, and the outcomes of investigations (i.e., whether the allegation was substantiated by evidence). Candidates' names can be submitted to these state authorities to search for founded allegations of abuse. (Allegations that were not substantiated by evidence might not be revealed.) No national repository of this information currently exists; it must be checked state by state.
Credit History: With verification of a legitimate purpose, organizations can set up an account either directly with a credit bureau or with an intermediary entity to submit candidates' names and Social Security numbers for a report of their credit history. This type of check requires the candidate's consent and is typically conducted only when a someone will be handling significant sums of money.