How can I teach definite and indefinite articles in a classroom setting?
Back when I was in first grade, my teacher used an activity where she had a set of differently-colored plastic butterflies.
She would call a student up and say, "hand me a blue butterfly." The student would give her any of the blue butterflies in front of her, and she would say, "thank you."
Then she would call up another student and say, "hand me the orange butterfly." Since there were multiple orange butterflies for the student to choose, they would be put in the situation of not knowing which orange butterfly she was referring to, since she used a definite article. When they handed her an orange butterfly, she would say, "no, that's not the butterfly I meant."
The idea was that saying "a red butterfly" included all the different red butterflies, since the indefinite article was used, but saying, "the red butterfly" allowed for extreme specificity, since the definite article was used.