As AP Biology (Evolution) is puzzling over Isolated Populations, here's a very clear, simple, understandable, and tangible example:

For instance, in your class, you are divided into two groups. One group moves to the next classroom and studies Biology and Chemistry with a professional advanced expert teacher like me😎, while your group stays in the original class. After several months, the group that moved to my classroom receives their scores with a bright + over their A's, and are obviously not willing to have any relationships, talks, or dating with the other group in the previous class who stayed behind, all of whom received D's. This is a clear example of an Isolated Population—where they are separated from each other forever, speciation has occurred. 💔

Some Types Of Speciation:

And here is behavioral isolation:

But by far the closest example to your classroom is Allopatric Speciation: