"I tried being calm and it didn't work"

You may have been here before. A book, or a friend, or your own regret told you to stay calm, and for a fortnight you did. You asked nicely, and nicely again, and kept your voice level through the fourth and fifth ask, and the table still didn't get laid, and you ended up shouting on the Friday anyway, with the added bitterness of having tried. Calm, you concluded, doesn't work with your children.

I'd look at what you actually tried, because I think it was the ladder with the volume turned down. What follows is my reasoning.

Calm asking, repeated, is still repeated asking. The child still received five signals, and the first four still had nothing behind them. The only thing that had changed was that the run-up was quieter, which from the child's side made it less clear when the real instruction was coming, and so there was even less reason to act on any of them. You'd removed the shout, which was the one rung that worked, and replaced it with nothing. Of course the table stayed unlaid. Calm was never the part that was missing. Follow-through was.

This is why the advice to stay calm fails so many parents and leaves them feeling worse. It treats the shout as the problem, when the shout is the last step of a structure. Take away the last step and keep the structure and you have a parent asking five times in a level voice while the pasta boils over, and then a shout that feels like proof that calm is for other people's children.

The quiet ask isn't calm asking. It's one ask, made close, with a small consequence that happens if it isn't done. The calm is a by-product. You're not gritting your teeth through repetitions, because there aren't any repetitions. You said it once and now you're either watching it get done or doing the small thing you decided on. Neither of those needs a raised voice, and neither of them needs you to feel serene. You can be irritated and still walk to the child, say the thing, and put the tablet on the fridge.

If you tried calm and it didn't work, that's useful evidence. It tells you the volume was never what made the shout effective, and it tells you what was. The shout had a consequence in it, which was the parent losing control, and that was the only consequence the ladder ever had. Replace it with a small, boring one that you can deliver in an ordinary voice, and the calm looks after itself.