Ha! What a reasonable assumption! But, our experience has been that now that MCPS has switched to Curiculum 2.0, there is no formal math pre-assessment at the beginning of the year. At our school, the administration acknowledged that there were no math assessements and that they were placing kids in math classes/groups in an ad hoc manner.
In 3rd grade, kids will take MAP-M for math group placement, but I don't know if that applies at 1st.