Coding classes in the Scottish Borders

Easter Sunday is set by a rule: the first Sunday after the church's calculated full moon on or after 21 March. The calculated moon follows tables, not the real sky, so the whole thing reduces to whole-number arithmetic with remainders. The learner codes two famous versions. One, often called the anonymous Gregorian algorithm, is a chain of about a dozen divisions and remainders. The other, by the mathematician Carl Friedrich Gauss, is shorter but comes with two special exceptions. Both are then compared with the Easter function in a well-tested Python library, year by year from 1583 to 4099.

Gauss's formula without its exceptions looks perfect for decades at a time, then fails. In 1981 it gives 26 April; the real date was 19 April. In 1954 it gives 25 April instead of 18 April, and the next failure is 2049. Only 23 years in more than 2,500 go wrong, which is exactly why the bug survives casual testing: try a handful of recent years and every answer is right. The two exception rules exist precisely to catch those cases.

With a trusted function, the learner can ask bigger questions. The Gregorian Easter pattern repeats only after 5,700,000 years, and a modern laptop can run the whole cycle in seconds. Easter can fall on 35 dates, from 22 March to 25 April. The most common is 19 April, 3.9 per cent of years; the rarest is 22 March, under half a per cent. Within 1900 to 2099, the earliest Easter was 23 March 1913 and the latest will be 25 April 2038. Fewer than a quarter of Easters fall in March.

Hunting down the rare year where the answer breaks is a skill no AI supplies, and it is why a Borders teenager should still learn to code in 2026. The longer argument is in why teenagers should still learn to code in 2026.