I believe your Agent may have misspoke or you misunderstood a comment your agent made. Attendance schools are assigned by the School District; in this case, San Ramon Valley USD. You cannot unilaterally send your child to any school in the County.
In addition, as can be seen at the San Ramon Valley USD website below:
"*Please note: Many schools and grade levels are impacted by growth and students may not be able to attend their resident school. Please contact your resident attendance area school for further information and to verify the address."
One way to facilitate your new home search is to take a peek at http://www.SchoolAndHousing.com
Based on property address, SchoolAndHousing provides attendance area schools (Public, Private and Daycares) along with useful performance statistics and other information.
They also have a mobile application, which is quite handy when you are viewing homes! Just access http://www.SchoolAndHousing.com
on your mobile phone to download the app.
Before making an offer you should call the School District to CONFIRM the schools the property will feed to!