It absolutely true that there is a range of normal for hitting milestones. But not walking by 18 months puts a child outside of that range: http://www.cdc.gov/ncbddd/actearly/milestones/milestones-18mo.html. Surely everyone agree that if a child isn't walking at some point an evaluation is called for? So how do you determine that age cut off? Maybe based on the generally accepted range of typical?
I have never met a parent who said they wished they had waited longer for an evaluation. I have met a few who said it turned out to be unnecspesary, but they still felt better safe than sorry. And I met a lot of parents (since my kid received services, I have met more parents of kids who received services than most people) who wished they had gotten their kid help sooner. I have heard repeatedly from therapists, educators and other parents that sooner is better when it comes to getting kids who are struggling with developmental issues help.
I have never met a parent who said they wished they had waited longer for an evaluation. I have met a few who said it turned out to be unnecspesary, but they still felt better safe than sorry. And I met a lot of parents (since my kid received services, I have met more parents of kids who received services than most people) who wished they had gotten their kid help sooner. I have heard repeatedly from therapists, educators and other parents that sooner is better when it comes to getting kids who are struggling with developmental issues help.