Isaiah has been taught not to get involved in drugs. However, he puts that aside and tries marijuana after he sees his older brother using it without getting in trouble. What best explains Isaiah's behavior?

This would be a simple situation of a brother following his older sibling.

Explanation:

I've seen this before.

Even though Isaiah has been taught by his teachers and/or parents not to use drugs, he will try it if he sees his brother trying it without the consequences he has heard of from his teachers and/or parents.

Unless the older sibling has done anything wrong in the younger sibling's eyes, the younger sibling will always look up to his older brother/sister. Even if the younger brother has been taught over and over again not to do something because of the horrid consequences that come with it, he will do it if he sees his brother doing the same without the consequences specified.

In other words : If the older brother hasn't been caught by anyone for using drugs, the younger brother will follow suit, or at least try to do the same.

Hope this helps.

answer; taking detailed notes during the interview;