My daughter is starting K at Doyle Elementary (Univ. City), which is a decent school (API >900, albeit many English second language) this Fall.
Same Kindergarden assessment. And, she also has been to Montessori till now. IMHO, this is just a test to see that ALL admitted students passed it i.e. are ready for K. So it’s just a bare minimum and it’s the official standard having to fit all sorts of school districts from Del Mar to… I dunno, something bad. Chances are that 99% of the kids of your Del Mar school know much more that and will pass it, but they are not rating them and they will mix them together. Just to weed out those that TRULY aren’t ready. Just my 2 cents.
Now, FWIW, I’ve heard the Kindergarden assesment at Torrey Pines Elem. (La Jolla) was quite rigurous even for a Montessori (my daughter’s best friend went there) – reading, writing, counting to 100, simple additions and all sorts of other skills. Torrey Pines Elem is/was #1 in API scores. Probably they will group the students differently based on their skills/knowledge, where the others don’t really care.