A 34-year-old woman posed as a teenager to enrol at a private Texas high school.
Longview police said Charity Johnson was arrested after telling officers she was "Charite Stevens".
She was being held in Gregg County Jail on $500 bond for allegedly giving false information to police.
Police had been called to a flat when the person Ms Johnson was staying with said she no longer wanted her living there.
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Police gave her a trespass warning.
The principal at a small private school in east Texas said Ms Johnson enrolled with a guardian in October and filled out paperwork indicating she was 15.
Police said she was 34, although jail records listed her as 31.
PA