The juvenile court erred when it summarily denied mother’s 388 petition based on subsequent evidence. The 3-year-old minor was found to be a dependent of the juvenile court based on mother’s alcohol abuse and mental instability. Prior to the six-month review hearing, mother petitioned pursuant to Welfare and Institutions Code sections 388 and 390 to set aside the jurisdiction order after a court-ordered psychiatric evaluation concluded mother was not mentally ill and did not meet the diagnostic criteria for alcohol abuse disorder. The juvenile court incorrectly characterized mother’s petition as an untimely new trial motion under Code of Civil Procedure section 659 and summarily denied it without deciding whether mother made a prima facie showing of new evidence or a change of circumstances, which would require a hearing on the petition. Since the court’s summary denial was based on a mistake of law, the appellate court reviewed the ruling de novo. The appellate court held that the juvenile court erred when it concluded that mother’s 388 petition was an untimely new trial motion. Filing a section 388 petition to terminate dependency jurisdiction under section 390 was entirely proper. Rather than evaluating whether a prima facie showing was made, the court summarily denied the petition solely on an incorrect procedural ground. Rather than speculating as to the juvenile court’s evaluation of the evidence presented in the petition, the court remanded so the juvenile court could make that determination in the first instance.