We are 100% confident that Alex would not be where she is today without all of the early intervention she has received.  Our genetic specialist told us Alex would likely not walk until she was 3-3.5.  A highly prestigious neurologist recommended that we look into a wheelchair, because although Alex would want to let go and walk, she would not be able to balance appropriately to do it.  Alex walked at 2 years and 8 months, her balance improves all the time and she loves running around chasing her sister! She is my over achiever :)  I am confident that was due to all of the early intervention we were able to provide. 

Unfortunately demonstrating this as a fact would require a study design randomizing some children with therapy and others without.  Clearly, it would not be medically ethical to knowingly withhold therapy from a child in need.  So a rigorous study has actually never been done.  However, although there are no concrete studies to prove this fact, medical professionals, therapists and parents will all attest to the importance of early intervention and the benefits it can provide.