Under Child Find act can school/headstart be liable for not properly screening child when suspected disability?

My son is 5 yrs old and now in Kindergarten. He was just recently diagnosed w/ selective mutism. He struggles at school socially, I addressed this concern with the headstart program last year, they continued to pass it off as shyness. He went the ENTIRE year witout speaking to the teacher and/or social worker. The headstart program is meant for "early intervention" yet no screening took place. I am concerned for other children who may be experiencing this same problem, tax dollars and/or county money is used for this early intervention program yet they are not properly screeniogn and/or detecting issues that are of concern. Please advise, any help is appreciated.