Anonymous wrote: SLP here. The preschool teachers are incorrect, by age 5 we want to understand 100 percent, but a child may still have a few tricky sounds. At age 4, 75%-90% understandable is acceptable. It really depends on the sounds that your child's having difficulty with at this age.
4s/5s preschool teacher here and I came to say this.
Based on the articulation errors you describe (s sound, some switching) it sounds developmental. That said, it doesn’t hurt to get an evaluation done. Where are you located? Your pediatrician should be able to refer you to a local resource such as Child Find.