Based on the data displayed in the box plots, Mr. Simpson's class lost the most pencils overall. This can be determined by looking at the median value for each class, which is represented by the line inside the box. The median value for Mr. Simpson's class is 14.5 pencils, while the median value for Mr. Johnson's class is 11 pencils. Therefore, Mr. Simpson's class had a higher median number of pencils lost.
The spread of the data can also be considered, but it does not necessarily indicate which class lost the most pencils overall. Mr. Simpson's class has a narrower spread than Mr. Johnson's class, but this only means that the data in Mr. Simpson's class is more consistent, not that they lost fewer pencils overall.
Therefore, the answer is: Mr. Simpson's class; it has a larger median value 14.5 pencils.