attention and focus

Can anyone help me with ideas and methods that you have used with your children to keep them focused on their task.My son who is 8 years old comes home with complaints that he is not finishing his work on time in class. He knows what he has to do but won’t focus .When he is done with his work they are right but he finishes it very slow compared with his friends.If i offer him a reward he finished really quick. But this won’t work in school. My 4 year old will finish fast or gets distracted fast. I really don’t know how to keep them focused in one place till their homework or school work is done.

Any one who has some ideas that has worked for them with their children pls. help me please.

My oldest (9) is a daydreamer and I have tried many many things! Only a couple worked. The best one for school BY FAR was sending her to school with a sand timer. She can set it on her desk and turn it over and try to beat the timer to finish her work. Often she and whoever is next to her both race the timer and get the work done. She is naturally quite competitive but I think the timer just gave her some focus. Plus it only requires focus for a short period of time and she can clearly see time slipping away!
For homework the rules are simple. Work before play! So edays her stuffing around means she misses out on a play. Last week she was well behind on her math so I told her she had to finish two sets worth before she got to have a swim. Boy did she try hard! It was a hot hot day. She got into the pool 5 minutes before she had to get out but she earnt her swim!
I worked with teachers to find other solutions…short stints of work with reading in between, moving her desk to be by herself, bringing home unfinished work. None were all that effective. But a firm expectation of completion was very important over every thing else. Good lucj