Academy manager Bentley has left after 14 years of service while Jules, who also played for the Spireites, has had a 17-year association with the club.
Chesterfield chief executive Chris Turner paid tribute to the pair.
He said: "Dave and Mark have both provided the club with tremendous service over the years and I'd like to thank them for their efforts.
"It's always a sad day when people leave after being at a club for a long time. I'd like to wish them both all the best for the future.
"Supporters can be assured that we're still as committed as ever to developing homegrown talent."
Bentley and Jules follow assistant manager Tommy Wright, reserve-team coach Mark Crossley, development coach John Dungworth and kit man Kurt McDermott through the exit door at the Proact Stadium as the npower League Two club reshape their backroom staff.