Disparate findings on whether students attending charter schools outperform peers in traditional public schools (TPS) may stem from mixing differing types of charters or inadequately accounting for pupil background. To gauge prior family selection and heterogeneous effects, we distinguish between conversion and start-up charter schools, along with a third site-run model operating in the Los Angeles Unified School District (LAUSD). We find that TPS campuses converting to charter status (conversions) attracted more experienced and consistently credentialed teachers, and served relatively advantaged families, compared with newly created charter schools (start-ups), after tracking 66,000 students over 4 years, 2007-2011. Charters overall attracted pupils achieving at higher levels as they began a grade cycle (at baseline), relative to TPS peers, most pronounced among conversions that remained affiliated with the district. After matching students on their propensities to enter a charter school, we find that pupils attending charters outperformed TPS peers over the 4-year period. These benefits are most consistent and moderate in magnitude for middle school students. We observed significant though small effects in English language arts for pupils attending charter high schools. Latino students, mostly attending start-ups, enjoyed consistent benefits from attending a charter school.