2020-21 estimates are unreliable as they are based on data collected during the first year of the coronavirus (COVID-19) pandemic, when lockdown rules severely disrupted the data collection.
Er bod y rhan fwyaf o'r prosesau arferol dilysu data’r cyfrifiad ysgolion 2020 wedi digwydd, oherwydd y pandemig parhaol y coronafeirws, nid yw’r data wedi mynd trwy'r broses ddilysu derfynol arferol.