I live in Northridge also. If you go on the LAUSD website, it will give you information for finding the public schools that are assigned to your address. There are several really good public elementary schools in Northridge(with API scores over 800) but you generally have to go to the school associated with your address. If you want a different school, LAUSD does give you some options for transferring to another school. I recommend having someone from LAUSD speak to you to explain the process - it is a little confusing.
My son goes to Topeka Drive Elementary in Northridge. He went there for Kindergarten and is now in first grade. We are very happy with the school and they have great API scores. My mother is a special education teacher and she is very impressed with the school. We moved to Northridge because the public elementary, middle and High School assigned to our address all have high API scores.
Balboa Magnet is a great school but you need a recommendation from the Kindergarten teacher and "points" to get in. All LAUSD Magnet schools require points and they also have quotas based on ethnicity (ie a certain percentage of the school must be hispanic, a certain percentage must be white, African American, etc.) An LAUSD person should explain the point system to you as well. You get points generally by applying to a magnet school and getting turned down (we can apply to only one magnet school per school year). You also get points if your child has a sibling in the school, if you are a minority and for a few other reasons. Again, LAUSD should explain this to you because it is a complicated system.
I hope this helps.