I know it is his school work you are looking for but it may be useful for you to have access to all the school's records about him when preparing for his annual review. I found this on a trawl through information on the freedom of information act:
Educational records
Parents, and pupils who are 16 or over, have had the right to see local education authority (LEA) school records for a number of years. The DPA has now extended this right to younger pupils. There is no minimum age: any pupil who makes a written request to see their school records is entitled to do so, unless the pupil does not have the ability to understand what they are asking for. The right applies to any information produced by a teacher, an education welfare officer or an employee of the LEA. Access must be given within 15 days.
In addition to the general exemptions in the DPA:
Information likely to cause serious harm to the pupil or someone else's physical or mental health is exempt.
Information about a possible risk of child abuse can be withheld from a parent if disclosure would not be in the child's best interests.
Educational records can be inspected free of charge. Photocopying charges are limited to a maximum of £1 for the first 20 pages, plus a further £1 for every subsequent 10 pages, up to a maximum of £50. This maximum applies regardless of how many pages are supplied.
It looks to me that by denying you access to information that will help you ensure he can access to appropriate support in school, there may bea HRA (Human Rights Act) argument as well. I haven't got time to read the whole secion on "right to an education" but it might be worth your while going through it to see if there is anything you can use. Mentioning the HRA normally puts the wind up people anyway - it might be enough to get you what you need