My son at 14 is still a bit overweight (and has always been on the 99th centile for both weight and height before he started being overweight) He is dyspraxic which means that he is not only quite bad at sport but has some sensory issues which means he gets a lot of pleasure from chewing things/eating 
Looking back I think I could have done the following to improve things (although he IS much fitter and is now on the rugby team and walks everywhere) I feel my son IS growing into his weight now and still shooting up (already 6 ft) Tennis lessons, enforced group runs for D of E and D of E 20 mile hikes have also helped.
more protein and less carbs - lots of chicken meat and fish and far less pasta bread and potatoes
a sandwich when he came home from school instead of cakes and biscuits
a big pile of carrot sticks and cherry tomatoes to deal with the need to put things in his mouth
other chewy stuff - chewy necklaces, chewing gum (look on a SN board under sensory processing for advice and places to buy chewy things which aren't food)
Don't make a big deal of cutting down things he loves - children will always find a way to comfort eat and borrow pennies to buy sweets etc
emotional/self esteem issues unless dealt with are often medicated with food (cheapest way to feel happy) find other ways to make him feel rewarded - nice chat nice board game new music whatever
avoid sugary food -sugar high sugar low but don't make it an obvious cutting out just a cutting down replacing with stuff which is more nutritious
cut out sugary yoghurts completely and replace with plain yoghurt with a bit of honey and fruit
ditto juice - replace with sparkling water or plain water and fruit on the side.
Every time you walk somewhere with him you are helping him to feel fitter and giving him endorphins which mean he will desire less sugary/fatty food for the same rush.