Named skipper, 'Jacko' has led from the front for the reserves so far this season and has been outstanding of late in a central midfield role.
Camden-born and 21 on Monday, Jacko also looks back to his fighting weight after being set back by injury in the last couple of seasons.
Loan spells at Swindon and Colchester also helped last term and Colin believes the extra hours Jacko put in during the summer have paid dividend.
"Jacko's obviously worked hard during the summer away from the training ground and come back in good shape with a positive attitude.
"His manner and enthusiasm in training and the effort he puts has been great and it's good to see him get the rewards in the games.
"You can see the difference in him. You can see he's over the injuries that clearly affected him a couple of years ago.
"He's not felt sorry for himself and he's dug in, plugged away and deserves the praise he gets.
"But that praise means nothing - he has to do it time after time after time. He does well when he trains with the senior group and that's an indication that he's a good, good player."
Colin Calderwood believes prodigious young midfielder John Jackson is back to his best.