We are in public full day kindergarten. We have similar stuff craft centers to strengthen fine motor skills, letter sounds, rhyming songs, simple books, math activities that focus on counting to ten.
Based on beginning of the year assessments, the teacher has acknowledged that DS has already mastered most of the work -- pretty much everything except writing. I have let DS be my guide on asking the teacher for more.
He complained about the "math" and having to count to ten. I talked to the teacher. She did not like the extensions in the standard curriculum, i.e. count to 15 instead of 10. She did some research and tried to come up with more appropriate extensions that require him to group and manipulate. Still not terribly challenging but he's happy not to be doing "baby stuff." I'm confident went this is no longer enough this teacher will hear me and keep moving on.
Similarly, when he started to complain that books were too easy, I had a conversation with the teacher. The level of books changed to something more appropriate. Also, the teacher signed him up for a pilot computer program that allows him to progress through online books at his own pace (it sounds similar to Starfall).
In writing, teacher told me that she thinks DS can do more than he lets on and has noticed some perfectionism issues. If she tells DS that she wants initial sounds at a minimum, he will only write initial sounds or complete words that he knows how to spell correctly. She acknowledges that she needs to phrase things differently to get him to take risks and write more. Honestly, I couldn't ask for more in a public school teacher/setting.