Final answer:
An effective antecedent intervention for Levi's screaming for his toy could be teaching him to use words or signals to communicate his desire for the helicopter and reinforcing this positive behavior.
Step-by-step explanation:
When Levi screams for his helicopter toy, a good antecedent intervention could involve altering the environment or circumstances before the behavior occurs to prevent it. In this situation, it would be beneficial to teach Levi alternative, more appropriate ways to request his toy. For example, teaching him to use a word, phrase, or hand signal to ask for the helicopter instead of screaming. Meanwhile, it's also essential to reinforce these positive behaviors by rewarding him when he uses the appropriate method to ask for the toy. Consistent reinforcement should help reduce the instances of screaming.