Do you know why you tell someone which street to turn on well before you get to the intersection rather than as they driver is passing it? Obviously because it allows the driver to safely make the turn rather than in a two-wheeled, tires squealing fashion in a cloud of smoking rubber.
Teaching is like this too; if you clue in your students about what they will be learning about ahead of time, it is easier for their brains to pick out what is important. This idea is the core of Marzano's eighth element.
So, how can you (or an administrator who is evaluating your classroom) know if this element is being utilized?
I'm an 18 year veteran teacher that loves teaching, coaching, writing, and my family.