Lol! You have just described ds2!! He is that child - definitely minimum effort - he is super bright, so has always had the ability to coast slightly, and still get the grades. The drama we have to get him to do his homework is hateful - I must spend hours cajoling and reminding him it has to be done - probably takes him no longer than 20 minutes to do, but we have to have the huffing and puffing like Thomas the Tank Engine, beforehand. However, he has passed and will be going to a super selective in Sept so I guess he turned it on when he needed to. I do have to keep telling him that he will have to come in from school and do his homework, straight away, no arguing...ask me again in September if it worked!!
You have just described my DS, KCG - nice to know he won't be the only horizontal boy there in September!
Much like his mother, he will only put in any effort when its absolutely required