@NC2125 which LA are you under? If you'd rather PM me, do that. Different LAs have different systems to start the process of EHC Needs Assessment, so if you can tell us/me which LA, we can give you the exact place to go.
There are a few things you need to know:
1. Nobody is going to work as hard for your DS as you. Don't let other people control the EHCP process - you need to apply yourself.
2. If he is May born you can defer his entry to school but that doesn't mean that it's the best thing for every child.
3.The school can't insist that he's toilet trained, nor can they refuse to deal with him.
4.Support isn't dependent on diagnosis. It doesn't matter that you don't have a solid answer for why he's behind, they need to meet his needs.
5. Most special school places will be full now for this year because they were allocated in February. It isn't impossible to get a special school place but it's unlikely that you'll get one this year.
The basic process for an EHCP is this:
1. You ask for a needs assessment
2. The LA has 6 weeks to decide if your child meets the criteria [a) the child has or may have SEN b) the child may need provision from an EHCP] and to tell you their decision, giving you the right to appeal if they refuse to assess.
3. If they agree to assess, they have 6 weeks to assess your child. They must consult you, his current setting, and an Educational Psychologist. If you've already had SALT involvement, they will ask for their advice, and they may ask for OT advice.
4. By week 12, they must have all the information they need to decide whether to issue a plan, and if so, they have two weeks to write a draft plan.
5. By week 14 they must issue a draft EHCP, or inform you that they won't be issuing a plan and give reasons, giving you the right of appeal if they refuse to issue a plan.
6. You get a minimum of 15 days to look at the draft and make comments on it. You also get to name a preferred school. They have to name that school unless it is unsuitable for your child's age, ability, aptitude, or special educational needs (SEN); Incompatible with efficient education of others: Your child's attendance would negatively impact the education of other children, and there are no "reasonable steps" the school or local authority can take to prevent this; Incompatible with efficient use of resources: Placing your child would result in an unjustifiable or disproportionate misuse of financial and administrative resources.
7. If they agree with your preference, they will consult with that school. If they disagree, they will consult with the school you have named and others who they think are suitable. Those schools will tell them whether they think they can meet needs.
8. Between weeks 17 and 20 (and no later than week 20) they must issue the final plan, naming the school he will go to, giving you the right of appeal if they haven't named the school you think is right for him, or you disagree with the contents of the EHCP.
In practice, if you applied today, you'd get a Final EHCP on 14th September. So you need to get going. I would be urging you to apply today because that will trigger the above timeline.