According to Official Guinness Records,
The largest ski lesson was attended by 594 skiers who were instructed by Hansjürg Gredig (Switzerland) of the Swiss-Snowsport School at Sarn-Heinzenberg (Graubünden), Switzerland, on 23 February 2008. The lesson was 1,300 metres long and took 16 minutes. Although Hansjürg Gredig led the lesson there were supplementary instructors for every 20-30 people to ensure the lesson was being followed correctly.
For a complete list of 2008 records, please visit 2008 Guinness Records in Switzerland.