I'm a school and clinical psychologist.
For most kids I evaluate, a school eval does the trick and there are diminishing returns from a lengthy and expensive private eval.
If your child is particularly complicated, or maybe has a subtle presentation and may not require special education, or if an official diagnosis is important to you (in the school I can say "it looks like dyslexia but it's not official) then the private pay route may be the move.

We had good experiences with eval at our DC charter. But it’s contracted out.

Many people have had bad experiences with mcps paych evals-- they are not thorough and often miss things.

I’m in NY and here they are two separate things. A school district evaluation isn’t going to diagnose your child with X, Y or Z. They’re going to note behaviors and issues that prevent your child from accessing the curriculum at school, and they will assign supports, accommodations and modify classroom settings to make sure they reach grade level. That’s it. It’s support at school to reach grade level.

A private neuropsych is going to assess your child, provide a diagnosis and recommendations for more end to end treatment. They will say well your kid has dyslexia, adhd and dysfalcua. We recommend these private therapies, medication, these classroom settings and accommodations in a public school, or these private schools. And they will help you build your team of specialists by referring you out to the psychiatrists, schools and therapists they recommend.

Does that make sense?

I think it does not hurt to ask MCPS. If your child already has an IEP, MCPS has acknowledged your child's needs already. I think MCPS staff are committed to helping children. I know several families in our community that are very happy with the support MCPS has provided their children. If you aren't happy with their testing you can always request an independent evaluation.

Also definitely pursue what you can through your private insurance. It is different in scope and worthwhile if you have concerns outside of what falls under the MCPS evaluation.

Mcps did ours and the 3 involved were super nice. Talked me through the whole process.
My kid was in 6th in private and the resource teacher brought her concerns to us and filled out the required paperwork. MCPS diagnosed her with ADHD and said she is eligible for a 504 plan, her school just calls it an accommodation plan.

I talk to a MCPS special educator (not my child's home school), and she questions me why I not insist or request MCPS to do testing on my IEP child if I have concerns for learning disabilities. I already paid last year for a neuropsychological evaluations, but I am told that she was too young to be evaluated for learning disabilities at age 5. I have never thought of asking or request MCPS to do evaluations because I always have the thought they MCPS staff are too busy, MCPS are under budget, and they may not do a detailed evaluation due to either self interests or lack of resources. If I need to , I will just go paying private to get the evaluation done and present mcps with reports. DC has IEP since age 3. I thought Mcps cannot diagnosis my child because they are not medical professionals.

Am I right that paying out of pocket children hospital neuropsychological evaluations is way better than the one done for free at MCPS?