RobocupJunior のHPからリンクしている Wiki に世界大会のチームについての記述が掲載されていましたので、コピペしておきます。
Teams
Every year, RoboCupJunior attracts participating teams from around the world. There are over 35 regions with active RoboCupJunior activities. Those participating regions have established a process to select teams representing their regions at the annual RoboCupJunior competition held in early summer. To find out more about the regions and their contact, visit the RoboCupJunior community website:
In 2015, there were 161 teams and 677 students participated in RoboCupJunior 2015, Hefei, China. The team and students participation break down by league/sub-league can be found:
In 2014, there were 192 teams and 780 students participated in RoboCupJunior 2014, João Pessoa, Brazil. The team and students participation break down by league/sub-league can be found:
In 2013, there were 206 teams and 907 students participated in RoboCupJunior 2013, Eindhoven, the Neterlands. The team and students participation break down by league/sub-league can be found:
In 2012, there were 209 teams and 796 students participated in RoboCupJunior 2012, Mexico City, Mexico. The team and students participation break down by league/sub-league can be found:
In 2011, there were 251 teams and 955 students participated in RoboCupJunior 2011, Istanbul. The team and students participation break down by league/sub-league can be found:
世界大会の参加チーム数や参加人数の情報が2011年以降しか無いのが残念ですが・・・
この数字を見ると、2015年の世界大会は、チーム数も参加人数も、減らしているのが判ります。