schools and pdd diagnosis question

my son is 3.5 and recently diangosed with pddnos privately at the advice of his pediatrician. the school is upset we went private andnot thru them, and they want to retest him. one district that i thought we were zoned in was willing to take him on those tests, finish the ot eval and speech eeval during the 30 day trial period. the school district it turns out we are zoned for is the one dragging feeet. legally thjey have 90 days to get him in a program and apparently they plan to take their sweet time. is there a law or number for the 30 day trial period? anyone know?