At least, that is how the children see it.
It begins with the big demo or video clip. Amazing! Wow!
And THEN teachers expect learning! In the students' minds the thoughts are "Why? We've already seen the good stuff. Couldn't care less about the boring stuff." They then tune out and turn off.
Or an extremely brief introduction and then the practical. Great, playtime!
The students don't really have any idea of what they are looking for, so they don't see it. Then the lesson goes on to reason out the thing they couldn't see or relate it to something else they couldn't see. But it was nice playing with the equipment.
So what to do?
Build up to the climax. End with the Wow!
This is, sort of, done with the POEE or PEE, or whatever the letters are, format with demonstrations and it is not those I am talking about. I'm talking about the really big ones. If you're doing displacement reactions, end with Thermit (or my slightly different version that sets off the fire alarms). The lesson builds up to that point and that Wow point glues a great big memory label on the neurons, sticking down what went before. It doesn't work the other way around.
Practicals also work better when the students know what they're looking for. The 'Yes!' at the instant they confirm or disprove their earlier thoughts and reasonings is far better as it is emotionally laden and occurs during the experiment. Another great big memory label slapped down. Faffing about with results and finally 'discovering' a relationship is more of a 'yeah, right' moment and not very memorable.
My point? Lessons should work up to a climax (or a series of smaller ones dispersed throughout the lesson)
Or you could end on a song.