You might suggest a meeting or e-mail between his second grade teacher and current teacher or between the Gifted Teacher and his current teacher. You're correct in the possibility that his current teacher might not "get him" as often teachers who didn't grow up gifted or around someone who is gifted don't. I know I likely wouldn't if I didn't have a couple kids of my own who are gifted or I didn't organizes gaming events for kids who are. Gifted children are the exception after all, not the rule....and public education is pretty much focused on "normal" and bringing up the bottom.
It's important for any teacher who has a gifted student to understand that keeping that child engaged and challenged with appropriate pace, depth, and breadth is paramount to that child's success and mental health. Simply "Buckling down" and doing what is assigned regardless of it's content won't cut it for long, though as you said, it also has merit and is something anyone needs to learn as the world won't always conform to them.
Most teachers without training in gifted education also don't understand that an accelerated learner is always an accelerated learner. They grasp concepts in often 25% of the time it takes someone like me to do so and once they've grasped the concept their mind moves to whatever entertains it. That's often why such students seem to "Lose focus" or fail to be on task. Most GT teachers understand that, teachers without specialized training rarely do.
