LII is different at each school. My child has never been a reliable reporter of what is happening at school. He doesn't see the need to provide information about his day voluntarily and his answers to direct questions are brief. But he never discussed any pull outs for academics until LIII in 3rd grade, our school did not have LLIV and we choose to stay at the base for the immersion program and social reasons. Some of the worksheets we saw coming home included problems that had solutions with negative numbers and the like, I don't know if that was work the entire class was doing or LII worksheet.
K is boring for just about any kid who has had involved parents. The material that is taught is the material most of us are teaching at home. I suspect that the number of kids not being taught sounds and letters and the like is on the rise since I am seeing news reports that a lot fewer parents are reading to their kids today. K-2 is focused on teaching the basics. Kids who have been read to and encouraged to learn through play and don't have LDs/ADHD are likely to be bored by the academics at school. For some, learning the social norms is what is most important in K-2.
By 3rd grade, the kids who are smart and don't have LDs catch up to the kids who had a more academic home and the groupings sort of solidify. Since kids learn at a different rate, some kids will figure out school and how they learn and move into Honors and AP/IB classes in MS and HS. ES really is elastic in where kids are and doesn't really reflect where many kids will end up by HS.
We supplemented at home by reading books every night, watching documentaries that we thought were interesting and that our kid seemed interested in, think Planet Earth, playing board games that taught math skills and strategy. I was able to talk about mythology and history while DS was playing Mario because there are pyramids and sphinxes and other references that I would discuss with him while he played the video game. We did start math classes in 3rd grade because he was bored in math and that led to math competitions, which he still does.