It's critical to include objective measurement in IEPs. Without objective measurement, there is no FAPE, in my opinion. Without objective measurement, there cannot be a determination as to whether progress is being made. If one cannot determine that progress is being made, FAPE is being denied and it is incumbent on the school district to change their approach. Many IEPs do not include ways to measure progress objectively.
Schools often object to testing the child.
Go to the independent specialist or clinic that evaluated your child and ask them for to information about tests that can be administered quickly and frequently. Sometimes schools balk at using standardized measures because standardized measures are used more for evaluation than for tracking progress. I have a student with autism who has been given the PLS-3 for speech. When I talked to the speech clinician, she said that the PLS-3 can be given every 3 months. You can also use a standardized language sample.