|MadSci Network: Neuroscience|
Congratulations on your very interesting research project! In general, girls tend to have neater handwriting than boys at younger ages, simply because girls tend to be more calm and patient at younger ages, and therefore they will pay attention longer to their lessons, including handwriting practice. That is "in general," but there are some exceptions. It has been noted that gay boys may also have better handwriting, and "tomboys" (young girls with a lot of energy and activity) may have less clear handwriting.
Basically, "handwriting" is actually a direct representation of how the brain is thinking, so if the brain is calm and organized while thinking, it will show up in "better" handwriting.
Now, you also need to remember that people's bodies do not always develop at the same rate. Some people take a longer time to develop their fine motor (small muscle and nerve) coordination, which is necessary for detailed hand work, like handwriting. In the younger children, this is a definite reason why some of them might have more "messy" handwriting than other children, even of the same age. So, especially for the younger children, you need to look at their physical ability, not only their "psychology."
And, of course, some children might have physical problems when they are writing. There are children with neurological (nerve) problems, and other children with muscular (muscle) problems, and even if people don't see these things normally, it can affect their handwriting. Once again, you need to consider the physical abilities of the children you are testing.
Other reasons for "messy" handwriting can include children with problems in reading, problems seeing, and problems with learning disabilities, all of which can affect how they write, as well as what they write. In the early grades, there are a lot of "hidden" visual (eye) coordination problems that their parents and teachers might not know about. And some kinds of learning disabilities and reading problems also don't show up until later grades, since many of these kinds of problems do not really get noticed until the children are in fourth grade.
One more thing that you might think about. If you are testing children who already learned to write in another language, their handwriting will be different than the "normal" handwriting you are expecting to see. For example, the handwriting of a Russian, French, or person from another country often looks very different, even if they later learn to do "handwriting" in English.
In "general," your research project is very good, but you do need to know that there are some other things that might cause a "handwriting problem" for some of the children, whether or not they are "girls" or "boys." There might be psychological reasons, or physical development reasons, or even disability or cultural / prior language reasons, and all of these need to be considered when you do any research projects involving people. People are not simple! People are very complicated, and many things can affect their handwriting, not just their sex, age or grade level.
Try the links in the MadSci Library for more information on Neuroscience.