PP's questions are good ones.
My DC goes to an MCPS elementary school in Silver Spring. They are in 1st grade. They have very low support needs and don't have an IEP buy do have a 504 plan. I can't speak to DCPS at all. I will say I have been very impressed with the MCPS teachers DC has had so far. They seem to understand intuitively how to work with DC and we have seen them implementing the 504 accommodations very skillfully. I will say we did go through the IEP process in kindergarten, and it was an exhausting and frustrating process. I don't necessarily disagree with the outcome, but the process itself felt inefficient and confusing. The biggest issue we have had is just communicating with the school. Teachers are responsive, but other staff are less responsive. But DC is happy and learning, which is the most important thing.
One thing to know about MCPS is that the elementary schools with higher FARMS have smaller class sizes. My kid's K and 1st classes have been 16-17 kids, which I think has been very beneficial for DC. However, it does mean there are more kids with more needs at the school, which can stretch the school's resources.