A speech pathologist I worked with a few years ago taught kids to say "Oh, Man!" when they lost a game. She didn't say "It's OK to lose. Sometimes losing happens. Get over it" like I'm often tempted to say. She didn't prevent them from playing games so that she wouldn't have to deal with the emotions.
"Oh, man!" she'd say with full out honest. "Better luck next time!"
It was perfect. Those two words- oh man- let the kids acknowledge their disappointment in the game. They don't have to hide their feelings or listen to teachers lecture them on good sportsmanship. But they don't have to cry either. "Oh, man!" lets them communicate to us without a fit.
Basically it's replacing the temper tantrum/losing frustration with one phrase that will do the exact same thing for the child (let us know he is mad) without a great big fuss.
I use this with my daughter daily. I started to do it when she was just learning to walk and would fall down. She was shocked and surprised by the fall and needed a way to tell us. "You are OK" which is my first reaction- wasn't letting her say, "Hey Mommy, I just fell down and it sucked." It worked. She'd stop crying almost immediately and repeat "Oh man".
Now she does it herself without being prompted. She'll take a big spill, stand up, shake off her hands and say, "OH MAN!"
I've started using it when she wants something she can't get- like when I've left her favorite toy at home and we're in the car on the way to school, or when it is breakfast time and she wants crackers instead of cereal.
"OH man!" I'll say, "We left your baby doll at home! Oh, man!" I'm acknowledging how she feels and that the situation isn't ideal. I'm not solving it for her, we're not turning the car around- but I'm also not saying, "well, this is your problem to deal with." For whatever reason it works.
In fact, she's started saying, "It's OK Mommy" when I say "Oh, Man". She's stated her problem, I empathized with her, and now she can say it is OK.
Without thinking I started using this on kids at school too. They'll tell me something that is distracting/off topic/a very small problem and I'll look them straight in the eye and say, "Oh, man!" Like my daughter they often say, "Yeah, but it's OK. I'll do...." and describe how they'll fix the problem. Like suddenly they have to reassure me that it is OK they forgot their coat on the playground (even though it is math time and they know I'm not going to let them do anything about that now.)
Suddenly I'm not saying, "We're not talking about that now." or "How are you going to fix that problem?" or "Next time you should do x, y, z." Two words and I've communicated that
1)I heard their problem
2) I get why they are upset/worried
3) I'm not going to fix it for them
I don't always remember to do this. Yesterday I sat with a math group and was constantly saying, "We're not talking about that now." "Get back to work" "What will you do next time?" I showed no empathy and instead we wasted a lot of teacher-talk on redirection.
I know it won't always work, but so far those two little words seem to be working surprisingly well.