So when the bell rings, I really do expect the kids to find our classroom as quickly as they can. Dilly-dallying is illegal. The past two years I've discovered a little trick that seems to help with many of them. I've taught them to say, "See ya!" (Just imagine the inflection in our voices too.) As soon as the bell rings, they say it to friends, swings, monkey bars, slides, etc.
After recess when I'm trying to make a point about being on time, especially to those who weren't, I'll ask the first kiddo who was in line, "How'd you get here so quickly? What's your secret? Please do share so everyone can be on time from now on." Their response? "I said, 'See ya.'" Yep, I figured so.
(No, that's not my whole class. In my dreams though.)