My DS1 has only just got dry at 3 y 10 months. Also starting school in Sept and we're still having trouble with poos so I feel your pain! 

DS has quite significant speech and language difficulties so we were advised not to get hung up on him telling us he needs to go, but to train him to go on a schedule.
A few things that have been going well for us:
We skipped the potty and went straight to the toilet with a step and seat insert
To get the first wee in the toilet we tanked DS up with loads of drink then sat him on the loo with books, TV etc and stayed there with them until a wee came out. Then made sure DS was aware of the weeing and made a massive fuss with chocolate buttons etc. Rinse and repeat until he had the awareness to go on command.
Bribes - chocolate buttons in our case. Also TV programmes on the laptop while sitting and trying for a poo.
All changes sat on the loo. We used nappy pants/pull ups and had DS pull them down like pants before sitting on the loo even if already wet/dirty. Then he had to pull up the fresh pair like pants and puill his trousers up.
We used a kitchen timer and took DC to the loo every time it beeped gradually increased the time interval between toilet trips using it.
Gina Ford's book about toilet training isn't bad if you ignore the rubbish about it only taking a week. Oh Crap! was an utter disaster for us.