Even at its most prestigious magnets, the L.A. Unified School District must choose students based on a point system, not grades or test scores. What counts most for magnet high schools is having been enrolled in a magnet for lower grades. Admission points for opportunities in elementary school are awarded for living where schools are overcrowded or students are predominantly minorities. Having been on a magnet waiting list before also earns points. Guidelines can be found at eChoices.lausd.net.
Applying to a public charter is relatively easy. There are no boundary restrictions. If a charter has room, it has to take you. If oversubscribed, it must usually hold a lottery to decide who gets in. The California Charter School Association (calcharters.org) has information about rules and schools.
Popular private schools have far more applicants than spaces. The best bet: Apply for the lowest grade; upper grades are full of previously enrolled students and their siblings. But there are exceptions. This year, for example, Flintridge Prep had 50 ninth-grade openings.