For students of all ages. Gotta wrap your head around primes? Here's how you can think of it so that it makes sense, rather than just learning a bunch of numbers as prime.

Definition of primes. 1 is NOT prime.
Use the Sieve of Eratosthenes to find primes up to 50

Teachers: this is a great primer for students doing the Sieve for themselves students often find written instructions for this confusing. Show them sieving the multiples up to and including 5 and they should find it a breeze! Get them to stop when they hit 50, then finish the film and they can check their work.

Segue D.I.Y on paper up to 100. They must keep this work to help them remember. They will eventually learn the first primes for themselves, but it's much better and more enduring learning to work it out and be able to look back and review through understanding rather than trying to cram it by rote.