Your last line is so important - " so we his parents and his teachers can be more understanding. " If a child does have ADHD or SPD, it is really important to know because the child really has difficulty controlling what they are doing. And his anxiety is very much a clue that something is going on. And until he is able to understand what is going on - that anxiety will only increase as he tries to do better, but keeps getting into trouble.
So definitely check out the SPD site - http://www.sensory-processing-disorder.com/ - as sensory will many times get mistaken for ADHD.
In terms of ADHD, this is probably one of the most informative sites - http://www.help4adhd.org/en/about/what/WWK1.
Let us know what you think. Specialmom monitors this site on SPD - http://www.medhelp.org/forums/Sensory-Integration-Disorder-SID/show/1396
; And I, of course, monitor this site. Together we have a lot of resources that can help you.