My son is only 2.5 so I can't really answer your question about the age at which kids learn to read and write here. Regarding curriculum, if you have a preference for the type of philosophy/curriculum you prefer -e.g. Montessori vs. play-based/Reggio Emilia vs. Waldorf - then that will help you narrow down your search here.
If you can't find a preschool you might choose to hire a nanny if you can afford it. Rates are about $16/hr for one child and $22 for two children. Many families share a nanny with another family.
Here are links for San Francisco school information you may find useful,
SF Unified School District Map:
Online School Ratings:
Oggi Kashi - 415.690.3792 direct
Broker Associate, Paragon Real Estate Group CA DRE 01844627
All data from sources deemed reliable but subject to errors and omissions, and not warranted.