You have not included enough facts in your question, but I can tell you need an educational lawyer.
Some of the best documentation will come from your independent observations in the classroom, and those of your evaluators. You also will need the data that is being collected in the clasroom. You will need to plot out which prong of denial of FAPE each document serves to prove. Some will go towards denial, some will go towards the failure to make adequate acaedmic progress, that in turn will go towards appropriateness of the current placement.
Lastly, you will need some luck prooving denial of FAPE is a great burden. Engaging an advocate or educational lawyer will help you marshal the facts so that a due process may be filed.
Ask your self in advance, what remedy do you want the Independent Hearing Officer to grant you? You will need to list this in your prayer for relief. Check out the resources available at wrightslaw.com or andrewcuddybooks.com.
Good luck and vote this answer up if you found it helpful
This answer contains information intended only for the use of the individual or entity named above and may be protected by attorney-client privilege or work product doctorine. However, the mere receipt of this answer, alone, is not sufficient to create an attorney-client relationship. If the reader of this is not the intended recipient or the employee or agent responsible for delivering it to the intended recipient, any dissemination, publication or copying of this answerer is strictly prohibited. The sender does not accept any responsibility for any loss, disruption or damage to your data or computer system that may occur while using data contained in, or transmitted with, this answer. Should the reader have any questions please feel free to contact Attorney Kotler at TBKotler@sbcglobal.net or 330-777-0065 Thank you and please indicate if you found this answer and / or the link(s) helpful.
You did not provide many facts, but I presume your child already already has an IEP. (It sounded like the school perhaps was denying special education eligibility.) Assuming the child has an IEP, if you are correct that the IEP specifies grades as the measure of goal achievement, then right there you have a pretty good argument about lack of progress even in the face of more rosy progress reports. If I were you I would not protest the low grades as those teachers have done you a favor with their honesty. More times than not, I have seen "inflated" grades so that the grades match the progress reports.
Have you presented your private evaluations to the Team? If you have not done so, and you present them to the school now, they have to reconvene the Team. You can ask the same question you are posing here: "How can one make progress while the grade average is going down?" Be prepared to have the school blame your child and to blame the home environment for your child's poor grades. Rather than argue about this, merely take notes of what the school staff said. A parent's conduct at Team meetings does count. Remember that FAPE is really a measure of progress in education consistent with cognitive potential. So, if your child has a language based ld and is of average intelligence and is still doing poorly, the conclusion you want to reach is that the child is receiving inadequate services. Another good measure of real progress is to compare a current evaluation's results with one done years earlier. I like Attorney Kolter's carefully planned approach to proving the elements of your case.
These cases many times are decided based on a battle of experts. You should seek legal counsel and/or an education advocate to assist you.