Marcie, don't do the chanlllenges, it can backfire. You're going to have the child who might find it difficult and will feel left out and will have adverse effects, feeling of being inadequate, and possibly the other classmates teasing, you won't know about it, but it will happen. I speak from experience.
I've pretty much ran the gamut of Tex's experience, even tried the time clock like Tova suggested, worked in the beginning didn't after some time. This is from the experience of my older daughter and my son.
Now my six year old is in Kindergarten, this is what her teacher does and it might be something to consider.
She gives her class a homework folder with work for the entire week. There's a calendar of the month, with instructions written in for each day's homework. For example, for Monday, the teacher wrote (not verbatim), today we're writing letter M, big M and small m and she asks the students to write each five times so as to practice their writing. Then she will list a word, and ask the students to either, name two words that sound the same as the one she wrote, or draw a picture of the word that sounds like her word. She encourages mom or dad to sometimes write the words for the kids to copy or list the words for them and read it together. This is from Monday to Thursday, then on Thursday night, you sign the next page, and return the folder on Friday morning with the child. In this folder is a sheet for us to list each book we read each night. When my daughter comes home on Friday, she has no homework. When she returns from school on Monday afternoon, the folder is back. So the teacher marks the week's homework over the weekend.
I'm not stressed, Amanda is not stressed and she loves, love doing homework! Doing it this way I believe, helps the parents and helps the student.
So far she has done three projects. The teacher gives us a week's notice and we usually get it done and present it to her the follwoing monday, so even if we don't have the chance to do it during the week, we have the weekend to get it done. She encourages the parents to work with the child so that they know what they are doing, not do the work for them.
At my daughter's and my son's school each student receives a planner they will use for an entire year. If the teacher needs to communicate with the parent, or vice versa, we write in the planner and then we either contact each other by phone or email. Recently my sons's Science teacher had some concern and we are working together to get my son on track with his work in that class because he was out for a bit because of illness and so missed some pertinent stuff and wasn't catching up. The teacher was also concerned that he wasn't paying attention and seemed distance when he was teaching so I had to put a stop to the length of time my son spend in front of the computer during the week when he was not doing homework and reinforce his good study habits. He hates to study and he hates homework, but he knows he has to get them done. What his teachers do, and he's in the 8th grade, they have study hall and they get their homework done at that time during school which is less stress for both of us. I noticed that the teachers here in Florida, work as a team, a group of five or more, which is great because all the classes are on the same assignments and one knows what the other is doing. Like with my son and Science, he was able to tell me what was happening with my son in the other classes because he talked to them as well. I appreciated that!