This is a good graphic that can be used by both teachers and professionals. It outlines the main developmental milestones that children who are typically developing go through so they can screen for red flags.
Social and Emotional Skills: What to Expect at Different Ages
The speech and language development is an important and individual process for every child. Early intervention, will help your child to avoid not only significant speech and language disorders, but also secondary effects, such as low self-esteem, reduced social activity, fear of communication and learning difficulties.