Hi Emma
Jeannemum has given you good advice, you do need to keep on..and..on at the SEN dept. What Jac should end up with is a statement of of his educational needs and the process to get this is called statementing. Here is what you need to know generally
http://www.direct.gov.uk/en/Parents/Sch ... DG_4000870
but it does need to be started early. There should be a SENCO attached to the school that should work with you (special educational needs co-ordinator).
In my daughter's day (she is now 21) it was practically impossible to get a statement before 7 years of age, however she was entitled to a one-to one at nursery and reception until she got her statement.
This may well have changed because my granddaughter is in the process of getting her statement, she is 3 and has cerebral palsy but unfortunately her mum has to stay with her as appropriate support is still not available.
This might also be useful to you
http://www.parentpartnership.org.uk/, they can give you impartial advice.
Bearing in mind, if Jac does get a statement it is reviewed every year, this does not "label" him in any way but will make sure that he gets the appropriate support so he can access the curriculum, that means someone to help him with his diabetes needs.
Good luck