Start with the sixth form and work down to nursery. Every year group gets fidgetier, so you need sharper timing to catch the smile.
1 · Call outPress Space when the student sits down to say your phrase.
2 · Watch the barA marker swings across the bar. The student only smiles while it is in the green.
3 · Take the photoPress Space again to shoot. Closer to the middle of the green scores more. A miss means a retake, and it scores nothing.