Avoid cultural references that might confuse ESL students:

The following text is the first part of the introductory paragraph to a question about car speed:

"The police used to measure the speed of cars on the road by having two PCs some distance apart using a stopwatch. One of them would stand and wave as a car reached him. When the wave was seen by the second PC a stopwatch was started. As the car passed the second PC, the stopwatch was stopped."

The question itself read:

"Is the car exceeding the maximum speed limit in Britain?"

The ESL student who asked for my help with this question was puzzled how a personal computer could stand and wave. He also had no idea what the maximum speed limit is in Britain.