This is the exact thing that caused DD9's issues in school to start and what causes her the most trouble still - all the "free" time with nothing to do because she has everything done. If someone doesn't find something creative and interesting for her to do then she will find something herself and they probably won't appreciate what she will find to do.
We try to make sure she always has a good book to read and she will usually read when she is done. However, even with a good book, sometimes she just doesn't feel like reading and ends up getting into trouble. The gifted teacher gave her a bunch of "Think Sheets" which were fun for DD at first, but she hasn't done any of them for quite some time now. She is also allowed computer or Ipad time when she is done with her work and that gives her something other than sitting and reading.
DD7 has told us recently that when she is done she gets to help the other students. I guess this has been going on for a while, but she had just never mentioned it to us. This is a double-edged sword to me, but she seems to enjoy helping out, so we will leave it alone for now.
I agree that it might help to talk to the teacher to come up with some different options for your DS during his "free" time. One thing that was mentioned to us would be having DD come up with a project she wanted to do or a presentation she wanted to make to the class, then when she is done with her work she could work on her project or presentation. This would still be academic and gifties seem to like/need learning the in-depth knowledge that researching for a project or presentation would give them.
