When I taught K, I had several students over the 12+ years that I worked out with the first grade teachers for allowing my gifted reading children to go up for language arts/reading and then they came back into my room for the rest of the day. I didn't have a single negative comment made to me from either the end of the teachers or the end from the parents/child. The children didn't miss out on the "kindergarten" experience and in fact I saw a huge change in the gifted children that went out - they were much happier and I saw a huge difference in the boys in that I didn't see as many behavior problems as I saw before they got to move at their own speed for reading..they weren't bored anymore :-)