Socially Shy

I have a three year and 4 month old boy, who seems to withdraw from social settings when i am around.  We attend a music class that he refuses to participate in.  He'll sit on the floor and when the teacher approches him he'll either cross his arms and lower his head or make a don't bother me kind of noice.  Even when we go to the grocery store and people say hi he refuses to respond.  
He doesn't want to try new things and seems to negative about it.  Saying he doesn't have fun or doesn't like the teacher.  
I recently met a women who mentioned Sensory Intergration dysfuntion.  I really don't know what this is and if I should have my son evaluated or not.  
Just recently he has start to throw tantrams over taking a bath.  He'll scream and kick and refuse to take one.  I can't even figure what has triggered this reaction.

[Kevin Kennedy, Ph.D.]

There really is nothing in your description that indicates the likely prospect of sensory integration problems. Such difficulties involve the ways in which the brain processes the varied intricacies of sensory (hearing, vision, touch, smelling, taste) experience. Occupational Therapy is the discipline that evaluates and treats such problems. It sounds like your child is shy/reticent in his social interactions when you are present. One thing to consider is to 'make yourself scarce' at these times, so that your presence does not have an inhibiting impact on him. Sometimes such children actually surrender some of this reticence when the parent is not present.