Autistic or not autistic?

Well, I know this boy who is about 4 years old. He displays some signs of autism. He bangs his head with his hands side ways and recently, he drops himself on the floor which result in knocking his head on to the floor (from the back) which is very worrying. This happened because something does not go according to his needs (according to his mother, it's his way of throwing tantrums).
Another thing is his motor skills. When it comes to colouring, he can tell us where and what colour to colour the picture, but, he wants us to colour for him & he will be come when the colour is on the paper. So what I did was hold his hand and colour togather.
My main question is, how or what can I do to find out if he is autistic or not..

Thanks.

[chikp]

If you work at a preschool that this child attends, then you are in the right to want to make his day more successful and less disruptive to the rest of the group.  You are not, however in a position to diagnose this child.  There is a possibility that his mother has him diagnosed and in treatment and wants him to spend time with typically developing peers.  There is also a possibility that she is not concerned with his behaviors at all.  Either way, it is a private matter.

I think that the best thing for you to do is continue to come up with ways to help him complete his tasks throughout his day (like in the example you provided in your post about coloring).  When you tell his mom about his day, be honest but positive, "Well, he strongly resisted coloring today by hitting his head on the floor, so I took his hand in mine and we colored together."  Keep showing her all the things he is able to do throughout the day and describe the amount of assistance he needs and how it is provided.  She may start implementing these strategies at home!  If she brings up the "A" word to you, be prepared with the name of a developmental pediatrician or another appropriate source in your area and direct her to them.  

Sorry if this is not the answer you were looking for, but I hope it is helpful.