Today's Lesson Vol.46

The school year is coming to its end. The third year high school students had their graduation ceremony on Monday. Most of the third year junior high school students are taking their high school entrance exams today. Finally, the first and second year junior high school and high school students have their final exams this week.
We wish them all good luck!

Every year in English conversation classes, the first year junior high scool students make a speech. The topic of the speech is 'Memories of 6th Grade Elementary School'. The students show pictures and talk about their final year of elemntary school. It is very interesting.

Which idiom means good luck?