There is some variation in the characteristics of these schools, but all are fee-charging and most select their pupils based on academic ability or religious beliefs.
Ceir rhywfaint o amrywiad yn nodweddion yr ysgolion hyn, ond mae pob un ohonynt yn codi ffioedd ac mae'r rhan fwyaf ohonynt yn dethol eu disgyblion ar sail gallu academaidd neu gredoau crefyddol.