School task carried out in prison yard? (8)
I believe the answer is:
exercise
I believe this is a double definition.
'school task' is the first definition.
(exercise in a lesson)
'carried out in prison yard?' is the second definition.
(prisoners exercise in an exercise yard)
(Other definitions for exercise that I've seen before include "Do it to get fit" , "Gym activity?" , "Use" , "School task; drill" , "Physical training or exertion" .)