I'm constantly bumping into things and I often have scrapes and bumps and bruises on my body but can't remember how they got there. It's the same for my kids and it's all to do with spatial awareness.
Spatial awareness, which is often also referred to as motor clumsiness is the ability to think about a figure, usually your own body, in three dimensions.
Specifically it's about doing the mental calculations required to move your body through spaces without hitting other objects (unless you're hitting them on purpose, as in bat and ball games). It's not always about your body though because sometimes it's about other moving objects, like catching a ball for instance, or "extended parts" of your body, such as when moving furniture from one room to another without bumping into walls.
A lack of spacial awareness isn't one on of the defining criteria for autism and indeed I've seen some children on the spectrum with amazing ball control skills. It is however one of the more common problems I've seen.
Testing for Spacial Awareness Problems
Ball skills can be learned though, with practice and once your child has mastered these, it doesn't follow that their spacial awareness problems are "fixed", it simply means that they have better ball skills.
Another test is to test your child's ability to make their way through a maze. Of course, mazes aren't easy to come by (except on paper) so unless you live near one, it's unlikely to be a test you can complete.
There's an online test here which I found very difficult and in which I only scored average. It could account for my poor spatial awareness. I don't have enough information to say whether it's a good test or not but it is similar to other spatial tests I've seen. I would expect this test to be far too difficult for children.
Improving Spatial Awareness
Your spatial awareness isn't a static skill and even though it's common for people with aspergers to be a little "behind" it's something that can be improved on with a little effort. The best way to improve this skill is to use it. For children, this means getting off the computer and using this skill in real life.
Obstacle courses are a good starting point and you don't have to join the army to use one. You'll find obstacle courses at scout centers and camp sites and of course, if you're savvy, you can make one yourself. Other things that can help to improve spatial awareness are things like climbing and body awareness sports like Karate.
If nothing else, improving your spatial awareness could save you a few bruises in the future.