Magnet schools draw from all over the city to provide a more diverse student population & give students options outside of their neighborhood schools. It's a pure lottery system with a percentage going to "proximity" (1.5 miles from the school) and a percentage to the rest of the city --- all after siblings are admitted. Magnet schools usually have a focus like technology or arts that is incorporated into the entire curriculum.

Magnet doesn't automatically mean it's a 'great' school. Some are, some aren't. Do the same research you would do with neighborhood schools.