Honestly, many schools are uninterested in a parent's assessment of their child's abilities. Keep a record if you feel a need to watch progress, but the schools aren't going to use this information to assess placement. They may be likely to disregard it in fact, as a typical parent assesses their child's reading for example at a much high level than the school, and this is even the case for NT kids.
When you approach school age, it will be time to decide if you want to do early entry, regular entry, or skip K into 1st. This will depend a lot on non-academic aspects of your child. With the knowledge of what you hope to achieve, find out the legal requirements for your district (no early entry possible, for example) and see what you can work out (private school workaround). Find out if objective testing (IQ/achievement) will be helpful is achieving good placement.
My kids' school tests them regularly in school and have always come to me surprised by the high results. They didn't need me to tell them my three-year-old's reading level, with either kid.
In general, our advocacy has been most successful when the teacher sees the child's abilities and when the test results from the school's tests show high results.
