According to Official Guinness Records,
The largest fencing lesson (single venue) consisted of 300 people and was achieved by Premier Education Group and British Fencing (both UK), in Birmingham, UK, on 27 September 2017.The attempt took place on National Fitness Day 2017. The lesson was made up of pupils from Nansen Primary School and Rockwood Academy in Birmingham.
For a complete list of 2017 records, please visit 2017 Guinness Records in United Kingdom.