If you believe your child may benefit from an IEP, speak to your child’s principal. Depending on your child’s needs, disability or diagnosis, your child may need an assessment to support their needs.
An IEP is a working document that evolves with your child. They are generally reviewed annually and updated based on the needs and progress of your child.
Many IEPs are developed within the first 30 days of school (which is actually the mandate in some locations). Check with your state or provincial requirements.