Kids always want to "help" when they are too little to be effective and then balk at doing squat when they are big enough to actually be helpful LOL
With Beth and Luke being respectively 12 and 14 this year, we just tell them what we need them to do that day and a time frame to do it in. If they don't want to or can't be bothered to do the work (or do it properly) then we "can't be bothered" to run them to a friends, let them watch tv or use the computer or whatever it takes to get their attention. It's pretty normal at that age to want to skip out on chores or rush through them. Heck I did the "my room's clean mom!" thing at that age and everything was piled in the closet or shoved under the bed LOL.
I find with the kids if I can sort of give them a time line. Like..."I need you to clean your room today BEFORE 2 p.m. and BEFORE you make any other plans for the day". That way they have some flexibility to decide when to do it. Most of the time of course they leave it till 1:59 p.m. or 2 minutes before they want to go hang out with a friend but hey...as long as it's done it's done...or they can have a really boring day home with a crabby mom.
The worst is when they rush through it and do it badly. They hate and I hate having to make them redo it but if not they won't get the point to leave more time to do it right the first time.