Interesting how much some people think the onus is on the player himself to improve.
I stick up for Barkley a lot and my take on it won't surprise many, but I generally think there's a shared responsibility between Barkley and Koeman. That's generally because I think it's unrealistic to expect every player to be able to analyse their games and their flaws and how they can improve. That's not a slight on Barkley's intelligence either, there are many great players - Keane and Bryan Robson to name two midfielders - who have failed at management. Sometimes you just don't have those analytical skills or need some objectivity.
Koeman is right to demand a higher workrate; but I think the responsibility is on Koeman is to teach Barkley where and how to press. Koeman is right to demand more goals from Barkley, but he also needs to sit Ross down and say "you could have shot here; when the ball was wide here you should have made a run into the box" etc.
I don't have any real faith that Martinez was doing a lot of that, instead preferring players to play on instinct. Or if he was, he wasn't very good at it. I suspect Koeman does a lot more of it, but he strikes me as someone with less patience than most.
Obviously it's up to Barkley to fulfil these demands, but I personally felt like I saw enough from him December to April - especially when he had better players round him - to make me think he's listening and trying. If another year goes by and there was no improvement then fair enough, fuck him off, but at this stage I'd be doing everything I can to tie him down for another few years.