Endodontic management of immature permanent teeth with pulpal necrosis is challenging. It is critical that procedures are predictable, and that the affected teeth are preserved as long as possible for our young patients. Regenerative endodontic procedures (REPs) have the advantage over conventional apexification of supporting continued hard tissue maturation. However, it is unclear how frequently clinically meaningful root thickening or lengthening occurs, as well as whether clinical or patient factors can predict this outcome. In this presentation we will discuss results from a multi-centered clinical study, reporting the predictability of continued hard tissue development after REPs, and identification of specific factors that predict successful hard tissue maturation. We will also discuss the predictability of clinical success in teeth treated by REPs versus conventional apexification.