I had this issue with my almost 10 year old. This is what works for us:
There are certain subjects she HAS to do in the am because she can't focus enough to do them after lunch. Math, reading and handwriting are her three.
I set up a workbox system. She does math first. After trying several curricula we ended up with Teaching Textbooks. She loves it! I put her on a computer upstairs from her sisters. It's a bit of a pain for me to walk up there if she has a question, but it's worth it because she has the quiet she needs to focus.
Then she does her independent reading, followed by piano practice, then handwriting -- we're using Draw Write Now. Finally, she does her Grammar sheet (I think it's called Daily Grammar.) She can do all of these boxes by herself. During this time, I work with my almost 6 and almost 4 year olds so, by the time my 9 year old has finished her first few boxes, the little girls are done schooling and ready to play. Then I do the subjects my oldest and I do together: spelling, history, science, Bible.
I made sure to schedule things in an "in-breath/out-breath" rhythm. Math is an out-breath, reading is an in-breath, piano is an out-breath, handwriting is an in-breath, etc.
This new plan has made a WORLD of difference for us!