A: How did your school’s soccer team do in their last match?

B: Thanks to a schoolboy error by the opposing team’s goalkeeper, our team will advance to the next round of the tournament.

Note: “Schoolboy error,” primarily heard in British English, refers to a very simple, foolish, basic, or fundamental mistake. The expression, first appearing in the 19th century, was associated with errors typically made by schoolboys in class, such as a grammatical mistake. For example: The math textbook had to be reprinted after several schoolboy errors were discovered in some of the equations.