This is a list of extant schools, excluding universities and higher education establishments, that have been in continuous operation since founded. The dates refer to the foundation or the earliest documented contemporaneous reference to the school. Claimed dates must be supported either by linking to a properly referenced article (any language WP) or else by reference here. Unlinked, unreferenced schools may be deleted.
Sixth century
The King's School, Canterbury, England (597)
Seventh century
King's School, Rochester, England (604)
St Peter's School, York, England (627)
Thetford Grammar School, England (631), first conclusive evidence (1114)
Royal Grammar School Worcester, England (685), first conclusive evidence (1291)
Beverley Grammar School, (contested) oldest Grammar School in England (700)
Eighth century
Sherborne School, England (705)
Willibald-Gymnasium, Eichstätt, Germany (c. 740), founded by Willibald
Fulda monastery school, Fulda, Germany (748), founded by Sturmi
Gymnasium Paulinum, Germany (797)
Gymnasium Theodorianum, Germany (799)
Ninth century
Gymnasium Carolinum, Osnabrück, Germany (804), founded by Charles the Great (Charlemagne)
Domgymnasium Hildesheim, Hildesheim, Germany (c. 815), founded by Louis the Pious
Stiftsgymnasium Xanten, Xanten, Germany (exact founding date not clear)
Tenth century
Wells Cathedral School, England (c.909)
Warwick School, England (914)
St Albans School, Hertfordshire, England (948)
The Minster School, Southwell, England (c. 956)
King's Ely, England (970)
Benedictine High School of Pannonhalma, Hungary (996), founded by Grand Prince Géza of Hungary
Eleventh century
Roskilde Cathedral School, Denmark (c. 1020)
Suzhou High School, China (1035)
Menntaskólinn í Reykjavík, Iceland (1056)
Viborg Katedralskole, Denmark (c.1060)
Katedralskolan, Lund, Sweden (1085), originally part of Denmark, despite the many Danish-Swedish wars continuously operating since it was founded.
Salisbury Cathedral School, England (1091)
Norwich School, England (1096)
Abingdon School, England (1100, endowed 1256, refounded 1563)
Twelfth century
St Paul's Cathedral School, England (1123)
High School of Glasgow, Scotland (pre-1124)
Reading School, England (1125 as the school of Reading Abbey, refounded 1486, Royal charter 1541, closed in the 1860s, re-opened 1871)
Royal High School, Edinburgh, Scotland (1128)
Stirling High School, Scotland (1129)
Stiftsgymnasium Melk, Austria (pre-1140)
Bristol Cathedral School, England (1140)
The Prebendal School, England (1116)
Ribe Katedralskole, Denmark (1145)
Trondheim katedralskole, Norway (c. 1152)
Bergen katedralskole, Norway (1153)
Oslo katedralskole, Norway (1153)
Derby School, England (1160)
Lycée Institution Saint-Malo La Providence, France (1161)
Westminster School, England (1179)
Exeter Cathedral School, England (1179)
Małachowianka, Poland (1180)
Lanark Grammar School, Scotland (1183)
Aarhus Katedralskole, Denmark (1195)
Paulo Pontine, later Bedford School, Bedford, England (Date Uncertain, refounded by Edward VI 1552, see below)
Thirteenth century
Colchester Royal Grammar School, England (pre-1206)
Metropolitanskolen, Denmark (1209)
Riga State Gymnasium No.1, Latvia (1211)
Thomasschule zu Leipzig, Germany (1212)
Ayr Academy, Scotland (1233)
Lancaster Royal Grammar School, England (1235)
High School of Dundee, Scotland (1239)
Bailuzhou Middle School, Ji'an, China (1241)
Harrow School, England (1243, Royal Charter in 1572)
Katedralskolan, Uppsala, Sweden (exact year of foundation not known, by tradition 1246)
Berthold-Gymnasium Freiburg, Germany (1250)
Johan de Witt Gymnasium, Dordrecht, The Netherlands (1253) (oldest school in The Netherlands)
Abingdon School, England (1256)
Aberdeen Grammar School, Scotland (1257)
Stedelijk Gymnasium van 's-Hertogenbosch, The Netherlands (exact year of foundation unknown, but first mentioned in 1274)
Cathedral School in Turku, Finland (1276)
King Edward VI Grammar School, Louth, England (1276)
Ruthin School, Denbighshire, Wales (1284)
King Edward VI Grammar School, Stratford-upon-Avon (1295 refounded 1553)
Stedelijk Gymnasium Leiden, The Netherlands (first mentioned 1323, but year of foundation is estimated mid 13th Century)
Fourteenth century
Stamford School, England (c.1309 but re-endowed 1532)
Northallerton School, England (1323)
Hanley Castle High School, England (1326)
Queen Elizabeth's Grammar School, Horncastle, England (1327)
Gymnasium Erasmianum, The Netherlands (1328)
Gymnasium Ernestinum, Celle, Germany (1328)
Gymnasium Laurentianum, Warendorf, Germany (1329)
The King's School, Grantham, Lincolnshire, England (1329) refounded (1528)
Bourne Grammar School Lincolnshire, England (1330)
Hull Grammar School, England (1330)
King's School Ottery St. Mary, England (1335)
Barlaeus Gymnasium, Amsterdam, Netherlands (1342)
Bablake School, England (1344)
Instituto San Isidro, Spain (1346)
St George's School, Windsor Castle, England (1348)
Ripon Grammar School, Ripon, North Yorkshire. (1348) Date is earliest record but the foundation may be much earlier (7thC) but continuity is uncertain.
Doncaster Grammar School / Hall Cross School, England (1350)
Beauchamp College, England (1359)
Sint Maartensschool (name later changed into Praedinius Gymnasium), The Netherlands (1375)
Prince Henry's High School, England (c1376)
Stedelijk Gymnasium Johan van Oldenbarnevelt, Amersfoort, The Netherlands (1376)
New College School, England (1379)
Wisbech Grammar School, Wisbech, England (1379)
Knox Academy, Scotland (1379)
Samuel von Brukenthal National College, Sibiu, Romania (1380) - originally part of Hungary
Winchester College, Winchester, England (1382)
Hereford Cathedral School, Hereford, England (1384)
Katharine Lady Berkeley's School, Wotton-under-Edge, England (1384)
Stedelijk Gymnasium Haarlem, the Netherlands (1389)
Halepaghen Grammar School, Germany (1390)
Penistone Grammar School, Penistone, England (1392)
Gymnasium Haganum, The Netherlands (1394)
Cathedral School of Vilnius, Lithuania (founded before 1397)
Ipswich School, Suffolk, England (1399) (first record of existence)