Homework helps to reinforce the ideas learnt at school, as well as to help students get used to the idea of always having work to do, such as adults do in the 'Real world'. It can be said that homework is a 'waste of Time' because it is seen as 'more work at the end of the day' or 'that the work should be done at school, if it needs to be done at all.' The purpose of homework is not to give the child 'more work', but to reinforce all the ideas taught to the student that day. Studies done in 2006 report that doing homework resulted in a 26% increase in grades. This SHOWS the productive and positive affects of doing homework.
"School kids jump for joy, and parents get ready to breathe a sigh of relief. A US study has found 'no relationship' between more homework and better grades." Here is a quote from the Australian Woman's Weekly, it speaks for itself. Now, you're saying that it will help students get use to the idea of having work to do, that happens at school already whilst you're learning. You also pointed out that homework reinforces what you've learnt that day at school, no school will only teach a subject for one day, you go over what you've learnt from the previous class and then advance in that area. There is no amount of homework that will make anyone smart. At a young age (Primary School) it's unnecessary for kids to be given homework, it will simply give them a negative attitude towards it in the future. Once you get to high school you should do revision for tests, or perhaps class work that you didn't finish. But other than that, having set homework that a teacher has given you is unnecessary.
Having set homework allows for your brain to have a necessary time it needs to memorize it, or 'set it in stone' for want of a better word. The study previously mentioned does not state that children get 'smarter' if they receive homework, but they do reinforce the idea in their mind. During time that will be spent in University, or collage in the states, we will have to study for whichever subject we eventually choose. If we only did work while in class, we would not pass our subject, forget getting a PhD. Homework is simply put 'work for home' and it is, but shouldn't be seen as anything more than revision for what has happened that day. Homework is designed to help the human mind remember more, using a technique called ELC; experiential learning cycle. This shows that we learn things through experiences, or from repeating things we may already know. This is why 'Practice makes Perfect'.
Here is another study for you "Recent studies in Australia have shown homework to be an unnecessary waste of time." This study has shown that there is no benefit at all for kids up to 3rd grade, and very little benefit for kids in grades 4-6, minimal benefits for students in grades 7-9, and some benefit to 10th-12th graders. Could you honestly say that homework is worth the strife that it puts families through for these little results. Particularly towards the start of high school kids have enough chores to do at home as it is, and then adding homework on top of all that can easily cause unnecessary stress. School to kids is the equivalent to a stressful job that many parents have. You wrote that if you only did work in class you wouldn't pass the subject, while that may be true, I said previously that some studying should be done at home as revision for tests. I'm not saying no work should be done at home, I'm saying that teachers should not give homework to students while they already revise, which causes the unnecessary stress I was talking about.