How to Homeschool Multiple Grades at One Time

I should really have titled this: 

"How to Homeschool Multiple Grades at One Time? -

 When they all need you!"

I have two 6th graders, two 3rd graders, a Kindergartner (who shall likely promote in January) and a toddler.  No, I have no twins, but God blessed me with girls born 15-20 months after their brothers.  Both girls are motivated and academic kids, both boys are ... boys.  So it works nicely to school them together.  Not sure what I'll do when my 6 year old 3rd grader gets much older, but that's a problem for another day.

By 6th grade children ought to be able to do most of their school by themselves.  And my girl can.  But my boy, who is very gifted with his hands and ability to think (except as it pertains to how to stay out of trouble), is not gifted with academic motivation and struggles with his reading still. 

So inevitabley, we start school with great intentions, but then the "baby" gets into mischief, the oldest can't keep himself on track, the oldest girl can't focus because someone is breathing, the 3rd graders are whining they need my help and the Kindergartener is happily coloring a picture.  Chaos ensues and we aren't able to keep up with everything we need to do. 

So I'm trying a new plan, I've pondered it for a LONG time, sure that it can't work.  But desperation causes willingness to try, and the desperate jump for any liferope they see.

I'm doing school in stages, setting aside time that each grade gets mommy, and the others are on baby duty.  They are responsible for playing with him, keeping him contented and out of trouble while I do school with the other grades.  Yesterday was the first trial day, and it was a shortened day, so that we only managed to get one grade done, so I can see problems arising there. 

I want to know, have any of you other homeschooling mommas tried anything like this?  If so, what were your experiences?