You wouldn't have a conviction, you'd have an adjudication. It sounds like you got some sort of juvenlie diversion. You might have a juv record, but no adult record.
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I agree with Mr. Feasel that you do not have a conviction. Based on the information provided, it appears that you were afforded some type of informal diversion pursuant to Welfare and Institutions code sections 601 et seq. where you had to take a class and stay out of trouble for a period of time through the probation department instead of filing a petition in Juvenile Court. If so, there was not any type of filing of charges in juvenile court or any type of adjudication. If you are now 18 or over and have not been in trouble since then, you should consider having the record of arrest sealed and destroyed. Contact an experienced juvenile delinquency attorney in your area or in some counties, the public defender's juvenile division may have a program to help individuals seal and destroy their juvenile records. Good Luck!