Where a minor committed under Welfare and Institutions Code section 602 prior to the adoption of Proposition 21 is later charged with a probation violation, the court may apply the reduced burden of proof under Proposition 21 to those probation violation proceedings without offending the ex post facto clause. Proposition 21 allows the court to apply a preponderance of the evidence standard to juvenile probation violations under Welfare and Institutions Code section 777, subdivision (a)(2). The new standard of proof does not result in an increased term under the original 602 proceedings, nor does it implicate the degree of proof required at the original adjudication. Thus, the amendments to section 777 may be applied to a minor committed under section 602 prior to the adoption of Proposition 21.