Best interest test rather than presumption of return test applies after 18-month review hearing to determine whether guardianship should be terminated. Mother filed a 388 petition to terminate the grandmother’s guardianship of her twin minors and return them to her with additional reunification services. The juvenile court granted the petition in part, ordering the Department to provide mother with additional services. After mother completed the services, one of the minors was returned to her. The other minor preferred to live with his grandmother and requested a contested hearing at which the court applied the best interest test and found it was not in minor’s interest to terminate his guardianship. On appeal, mother contended that the court applied the wrong test, and it should have used the statutory presumption of return test under section 366.21. The appellate court rejected the argument and affirmed. The court used the correct standard when it considered whether it was in the minor’s best interest to be placed with mother. The Legislature’s express preference is for using the child’s best interest to make custody determinations after the 18-month hearing, rather than the presumption of return test. Completion of additional reunification services does not guarantee that a child will be returned. Further, the court did not abuse its discretion when it found that it was in the minor’s best interest to remain with his grandmother.