R.P.
I am reading a great book called 'Screamfree Parenting' by Hal Runkel. I really recommend it. It tells you not to take the kids actions personally. Take a deep breath. They are not out to get you. That needs repeating. They are not out to get you. Be consistant. If you promise them a reward or a punishment, follow through. Even punishments are promises that need to be kept so they trust you. Say what you mean, mean what you say. Don't make consiquences something that is going to irritate you. And remember, the worst that can happen is that they repeat a grade without their friends. Make sure that they know this, but don't harp on it. It will take them some time to get used to the new system. It is not an overnight thing, but you will be surprised at how well it works. Also, make yourself available for homework help, but don't stand over them with the ruler. Let them make the mistakes. Remember, if you do do weekend rewards and one or more kids haven't preformed, leave them home with the sitter, or whatever. If you do a little work, you can spend more quality time with your kids. It is not all about quantity. Let them see that you working benifits the whole family, not just saving your sanity...=)
They are not out to get you, they are just testing the boundaries to see if you are being consistant. For Kids consistancy = Love.
Good luck
R.