Let me start by saying that I know we are very lucky. Our elementary gifted program is outstanding. That said, Kindergarten and first grade still only had ability grouping for reading in the regular classroom. Second grade added pullouts for reading and math a few times per week for those that tested into the gifted program via multiple ability and achievement tests (>98%). Kids can be accepted to just math or just reading. They don't have to qualify in all subjects but do get to participate in all subjects.
Third grade is when the fun begins with a separate gifted math class pullout daily. Our teacher is wonderful and he is the teacher of record for math and provides grades for report cards. 3rd also included more frequent reading pullouts and a special project class for additional differentiation. DD9 in 4th gets even better and we have daily reading, math. By 5th, the gifted teacher teaches all subjects and provides all grades with the exception of science.
He also facilitates after school chess and robotics classes. There are two additional gifted teachers but this one is a true gift to his students.
Great public elementary schools for gifted students do exist. Perfection? No.
Differentiation in the regular classes (social studies, science, writing in 4th) is still pretty much "help the struggling kids when you finish your work". But reading the stories on this site from some people help keep me grateful for what we do have.
