After struggling for quite a while with unfinished assignments, I finally came up with a workable solution. 

On a small stack of index cards I wrote the name of the common assignments given.  For instance, Math Worksheet, Bible Notebook Page, or Read Chapter(s).  Now when we have completed our time together, I select the appropriate "Que" cards and set them out in a central area of our house--one he will walk by many times throughout the day.  When he completes an assignment, he turns the card over telling me what kind of progress he is making.  This way neither one of us forgets what was to be done.  When he is to work on specific words for spelling, etc., I use a post it note on the card. 

This is working out really well!  It puts the responsiblity on the boy to follow through, and relieves me of having to continually badger him.  If he self-governs his time, he will complete his assignments in a timely manner.  If not, we review how time was spent and what would have worked better to get his "job" done.  (We often call "school" his "job"--as in, God has given him a special job to do at this time and that is to learn and use his gifts to do his learning the most excellent way he can.)