I have a 12 yr old 6th grade and most days we do. He is very goal oriented and wants to get the job done before he takes breaks. We do sort of a block schedule.He does 2-3 hours each subject. Monday is math, Tuesday is Language Arts, Wednesday is Science, Thursday is Social Studies, Friday is catch up or extra days. He then does spend about a half hour each day for what we call electives. He chooses which one that day and for how long.(Foreign Language, Technology, etc...) This does not include his hour or reading a day or his book he is writing, or co op classes, watching movies or field trips. These I consider extras and they are up to him to get done.
I don't think I could make his day any longer unless I gave him busy work. He already finishes most of it before the end of our school year. He is getting great grades so I don't see giving him more work to make his day busier. We don't use a formal curriculum. I piece mine together. Most of it though is bought.(Math is yourteacher.com I make him take the pretest if he gets a 100 he can go to the post test and if he gets an 80 or above I don't make him do the lesson 90% of the time he doesn't do the lesson. And when I give him tests the chapter tests he is getting over an 90. No sense in just keeping him busy.