I taught both in the classroom and now I have homeschooled my child since the 2nd grade. My child would do the same thing. If you are certain your child knows the subject concept and what is expected of him then perhaps you can use incentives.
Perhaps you can use a point system to earn a trip to the dollar store, movie tickets a day at the park etc.
1. Have specific expectations. For example points can be earned for: doing homework done neatly the first time (big points!)no complaining or crying when asked to do work more legibly, good attitude while working AND even give him a point when he is assisting his younger sibling in some way.
2. Never take points away.
3. Help him set goals
4. When he meets those, increase goal expectations as the year progresses.
5. Work with him to decide on the incentives.
6. Eventually phase out the incentives.
I also tried to instill a prideful work ethic in my daughter by telling her God made three times. Work time, playtime and rest time. When she would complain while we work working I would say.."This is work time,when we have done our appropriately you can enjoy your playtime." I had to repeat this over and over but eventually she knew, "ok, I am here to work right now."
Homework time can be emotional. Stay calm,firm and in control. Do not engage in argument with your child.Their goal is to break you down. Once you get angry or in an argument..you've lost.
Lastly, designate a Hall of Fame in a prominent area in the house where you can display his best work. (Don't confuse correct work with neat work) You cannot penalize him for work he has a challenge with....and if your child is on a traditional school schedule then Spring time may present an issue. Students tend to get lazy because they know the last few months of school remain and they are thinking about full time play in the Summer.
Best wishes! Hope this helps.