My current system...

          I came up with a system that worked for me. I've been trying this for a few weeks, and it's so far the most agreeable and flexible system I've used.

          Due to my increased workload in school, I've made it a point to allocate Monday to Wednesday afternoons to focus on things at work. This means that I will be back later in the afternoon, and will be exhausted mentally and physically. At night, I opted to relax and rest. On Thursday and Friday afternoons, I made sure I will be back earlier, to rest and to do school work with the kids. This continues onto Saturdays and Sundays. My boy has been very cooperative with the work assigned to him. I would explain to him what is
expected from the exercise, and he'd be off to finish them by himself. Then, I'll have time to help the girl with her work. 

I tidied their school bags everyday according to their school timetable. My son has only a few books, so he brings all to school everyday. As for my daughter, I sometimes have trouble to quickly finding her books. She has 2 stacks of books, one for the first half of the year, and the other is for the second half of the year. I did not want to put them away, out of sight. So I colour coded them. She has a few codes. The blue is for the first half of the year, blue with yellow in the middle is for the second half of the year, and green is for her workbooks at home. Extra workbooks for the second half of the year is tied up, but remain with the rest.

Every Thursday, I'll go through and ear mark all the books for exercises. The green is for my daughter, orange is for my son.

This is a simple motivational chart I use with my son. He is sometimes reluctant to do his work. This chart gets him going. He gets a yellow sticker for every book (selected exercise) he finish. When he managed to collect a row of stickers, he gets to do one activity he chose. Usually it's related to art activities. :)