I got 100% on my coursework, and an A* overall.
Although I did a different project (most people made perfume boxes in my class, and I made a home-donation charity box, point of sale display for leaflets and wristbands, plus the leaflets), I have a few tips.
Firstly, ensure you go into detail about even the little things, linking everything back to your target market and purpose. Eg, the font used, the safety information regarding the activity (where it is placed, font, size, etc etc), colours, themes, etc etc.
Secondly, try to use or at least test different materials in your experimentation stages. For example, try 3/4/5+ different types of adhesive when deciding how to put the box together or if you are having it folded in such a way that it stays together without glue, try different folding methods and ensure to stress the positive environmental aspect of not using adhesives.
Thirdly, spend time on your evaluation stages. My teacher, bless her, was having a tough time as her husband was struggling with a heart condition so we had to pretty much do the project all by ourselves - so I can see why you are asking for advice. We were left with about a week for evaluation, although I was the only one to finish on the deadline, so many had less time than that. Make sure you carry out extensive questionnaires, publish the results and display them in relation to other factors, such as how the safety aspects were viewed by parents or how colourful the children found it. Etc. Don't be afraid to be critical - there is nothing wrong with saying, 'in light of this research, I think the product could be improved by x, y and z'. However, be sure to balance, or exceed, this with positive comments linking it back to your original specification.
All in all, be detailed, be adventurous and enjoy it! I know the coursework can be hard going but there is something really satisfying about having a well made final product with an in-depth portfolio to back it up.
Good luck.
=D