My 9-year-old son is due to be excluded from school because of his behaviour within the class.   At home he is a normal intelligent young man, but for some reason he is not behaving within the School.

Perhaps the first thing that we need to do is to clarify your definition of  "normal".

When there is this amount of difference between the ways a child behaves at home and at school alarm bells need to start ringing and directing the parent's attention to the way they handle poor behaviour at home.   In particular, is there any behaviour that parents have become accustomed to that is unacceptable outside the home?

The parent's job is to fit the child for the real world outside the home not to fit them into a bubble of behaviour that is only acceptable at home.

He has a very fearful nature and as such will not respond to any sort of pressure to conform.

Isn't this a different way of saying that at home you cannot get him to do anything he doesn't want to do?

Perhaps there is a flaw in your analysis of your son's  "very fearful nature".   What you say here may be possible if your child's problem resides at some deep analytical level but parents always need to look at problems in a more straight forward way first.   It is not uncommon for strange behaviour to be given validity simply because parents do not have the skills to train it way.   If your son really has, as you believe,  "a very fearful nature"  then surely he would be more likely to conform when put under pressure.

This is sometimes mistaken as bad behaviour

Again, why move so quickly to this conclusion.   This analysis comes from the belief that your son is such a strange and unusual boy that extreme fearfulness leads him to be defiant.   It is just as likely that this conclusion is the mistaken one and that this is just  "bad behaviour".   In other words an interactive problem maintained by a parent who sees such behaviour as a personality trait rather than an area in need of training

I do acknowledge that due to his late development his social skills are not what they should be, which can cause Barry a lot of emotional problems.

Again, his "late development" may have been due to an unknown cause that also affected his social skills but late development itself is not a factor in the type of social skills that your son appears to lack.   Many children of three and four years have the skills that your son appears to lack so it is unlikely that his problems are connected to developmental age.

If he is missing social skills then he needs training and the first place for that training is in the home.   Your analysis seems to accept this lack of skill as inevitable rather than see social skills training as very much your daily task.

he seems to think that others should be able to cope with the same sort of verbal abuse.

My experience would suggest that this angry use of words to others at school is likely to also be happening at home and, if you are getting frustrated with him, you may also be using some angry words of your own.

He does know that this is wrong but for some reason he continues to continue with this disruptive behaviour pattern.

You say that he "knows"  that what he does is wrong but

"for some reason"   continues the disruptive behaviour.

I think you mean that he  "acknowledges"  this is wrong; in other words, you can get him to  say  that he understands this is wrong.   Many of my clients make the mistake of thinking that bad behaviour is about lack of understanding.   They get frustrated when their child appears to understand but still does not comply.

You do your son a disservice if you think that all he needs is moral information and then he will be able to use this to control himself.   Yes, it is important that your son knows the reasons why he should not do X or Y, but he needs something else far more.

Your son needs consistently and positively applied consequences if the inappropriate behaviour that you see at home is not to be repeated in school.   This is because another way of describing a boy that

will not respond to any sort of pressure to conform

is to say he is a boy that

must have his own way

and such a boy will not cope in school and will not make many friends.

It is possible that the quickest way to improve your son's school behaviour is through training at home.  I will need to talk to you further to be sure,  but if we both agree that this is needed I will be happy to help you with this task.