"Growing out of" preschool stuttering

Many of us who work with preschoolers see this situation often—you have a child under the age of three who is stuttering, and you can’t quite predict whether or not it’s a child who will “grow out of” the stuttering, or if it will persist. You wonder what to do regarding therapy, and you wonder how long to wait.
This article doesn't provide evidence regarding therapy, but it does provide us with some new information on the profile of children who do vs. do not persist with stuttering. The authors collected a large volume of language data from children ages 2 ½ to 3—some who didn’t stutter, and some who did (with a little under half who of those who would spontaneously recover). They found that, for the children who recovered from stuttering in the preschool years, as their grammatical skills improved, their disfluencies decreased. It was not age that decreased disfluency, but rather “greater mastery of grammar and syntax.” This relationship was not present for the children who persisted in stuttering, nor for the children who did not stutter. For children who would persist in stuttering, improvement of grammatical skills did not reduce their rate of disfluency.
Also there was no significant relationship between stuttering severity and whether or not a child would recover from stuttering. So, when you’re watching to see if a preschooler’s stuttering will improve, it’s perhaps not time that you’re waiting on, but grammatical development. And stuttering severity isn’t likely to help you guess the outcome.
Hollister, J., Van Horne, A.O., Zebrowski, P. (2017). The Relationship Between Grammatical Development and Disfluencies in Preschool Children Who Stutter and Those Who Recover. American Journal of Speech-Language Pathology, 26, 44–56.