How have counsel been found to have rendered ineffective assistance in a criminal case?

The People argue that even if counsel rendered ineffective assistance, appellant was not prejudiced. "[I]n cases in which a claim of ineffective assistance of counsel is based on acts or omissions not amounting to withdrawal of a defense, a defendant may prove such ineffectiveness if he establishes that his counsel failed to perform with reasonable competence and that it is reasonably probable a determination more favorable to the defendant would have resulted in the absence of counsel's failings. [Citations.]" (People v. Fosselman (1983) 33 Cal.3d 572, 584, 189 Cal.Rptr. 855, 659 P.2d 1144.) We therefore must determine whether appellant has made a sufficient showing that but for counsel's conduct, the court would have reinstated probation rather than sentencing him to state prison.