Whether using the original novels or the simplified editions for non-native speakers, Christie's books make excellent resources for the classroom.
Pre-teens find her mysteries aspirational, for many they are "my first adult read," and the murders and puzzles help maintain the motivation of older students through to the final page.
For non-native speakers the language is relatively simple and straightforward and detective fiction has the advantage of being a familiar genre. Also Christie and her characters are usually so well known that there is instant recognition from students.
Additionally, the existence of numerous film and TV adaptations offer easy to access extra classroom resources.And Then There Were None is probably the most popular book and is used especially for summer reading programmes in the US. Other recommended books include Murder on the Orient Express and The ABC Murders – a serial killer novel with a difference.
HarperCollins in the US have recently released two comprehensive teaching guides for Murder on the Orient Express and And Then There Were None
Students may also appreciate:
Spark notes for And Then There Were None (free to access online)
Spark notes for Murder on the Orient Express (free to access online)