Mae'n bwysig cofio bod y System Genedlaethol ar gyfer Categoreiddio Ysgolion wedi'i datblygu ar y cyd gan Lywodraeth Cymru a'r consortia addysg rhanbarthol.  Gwnaethom gydweithio i ddatblygu'r system ac rydym wedi mynd ati eleni i barhau i wella'r system ac i addasu rhywfaint ar y metrigau a ddefnyddiwyd ar gyfer y data. Oherwydd hyn, mae'n anodd cymharu canlyniadau eleni'n uniongyrchol â rhai'r llynedd. Cafodd y metrigau newydd hyn eu trafod gydag awdurdodau lleol, consortia rhanbarthol, penaethiaid ac undebau.
It is important to remember that the National School Categorisation System was developed collectively with regional education consortia and Welsh Government.  We worked jointly to develop the system and have worked further this year to continue to advance the system and to make some adjustments to the data metrics used and as such direct comparison with last year’s results is difficult. These new metrics were discussed with local authorities, regional consortia, head teachers and unions.