Some districts have street by street directories, and even #s go to one school, and odd #s to another school, so it's not always easy.
Then, once you know where the child will normally go, we have an impacted school situation in many of the desirable districts. In these situations, the child may start at the school that the district has an opening for the grade level and may or may not move into the "feeder" school when an opening occurs.
Typically if you enroll in March, and you live in the school's boundary zones (or January for Cupertino for instance) you have a great chance of getting into the feeder school. However, if you enroll now, you may or may not. For instance, let's say your child is in Noble School enrollment area in 95132 (that's where my children go). But you didn't enroll your child in the spring. Now let's say the school has three third grade teachers and all three third grade classes are filled with students. They may have to put you in a nearby school and if/when a third grader leaves, you could be on the waiting list to be accepted.
Also -- just when you think you know all the rules, different schools have variable rules. Like, there are magnet schools that have lottery systems for allowing students to attend because they are so popular.
Finally, be sure to call the district or school yourself to determine their rules. Because even your realtor may not know the exact 2012-2013 school year guidelines. My current principal will bump a different child to let in a child who is in the boundaries. But previous principals would never bump a child who has been in a school for three years just because a new child moved into the area. So, the rules change and the guideline interpretations differ by principal, district and school.