I started the DofE while I was in the Air Training Corps. Did the Bronze and Silver while I was there. Most of it was completed at weekends etc especially the volunteer work.
I did the Gold in 6th form though, so quite a bit of that was completed in school time.
Not sure how your school time table system works, but mine was 6 periods a day. And each subject had 6 periods a week. So while I was taking an AS I had 6 free periods, and after I dropped it I had 12. Very useful to get the homework done in
as most evenings were spent out with mates or the GF of the time.
Jamo