The third year is something of milestone. You're done with the first year learning curve where your getting your bearings and learning the lay of the land. You have no reputation to precede you and must forge one. It's serious business--because you get it wrong and you'll be undoing those mistakes for years to come. Second year, you're solidifying your gains from year one, but there's still a fair amount of getting situated, as in many classes you are teaching new content. You've known most of the kids only a year as the school year starts, and while the kids may know what kind of ship you run and what your expectations are, they're still getting to know you.
Third year, though, is where you finally hit your stride. You are finally firing on all cylinders and now have the wherewithal to start figuring out how to raise your game, to take it to the next level. You are past survival mode and your are seeking to thrive. Your eighth graders will now be students you've been working with for going on three years and you have a different kind of relationship, one that's been growing over years instead of months. Even the new students benefit from the third year boost. They are "grandfathered in" as it were, and reap the closer connection right along with the veterans.