There is an international summer school that happens in St Andrews every year. Students from several countries come and get a taster of Computer Science as well as other schools before they decide what they want to do at the university.
I talked to them about different sorting algorithms, the trade-offs between them. We did some sorting by hand using printed out cards with numbers on them. I hope the students both enjoyed the experience and got a bit of an idea of the kinds of things Computer Scientists work with.