To help decide if a sentence needs a period or exclamation, I first explain what a command is and give examples. Then I explain that an exclamation is a statement said with excitment or storng feeling. I give examples of that.
Then I tell them the exciting part... Hidden in the room are notecards. On each notecards a sentence is written. When they find it, they have to read it and decide is it a command or an exclamation? They each have a piece of paper, divided into two parts. One side is for commands the other for exclamations.
When they are done, we check it together.
Easy and fun!