Stephen Farrand has crafted a list of summer immersion programs for classicists. If you have any to add to this list, please send me a note! Here we go:
http://expressfluency.com/product/latin-teacher-training/
http://www.latin.org/programs/rusticatio/tironum/
http://www.latin.org/programs/rusticatio/veteranorum/
http://www.latin.org/programs/pedagogy/
https://mcl.as.uky.edu/conventiculum-latinum
https://www.umb.edu/academics/caps/summer_programs/institutes/latinbysea
http://www.dickinson.edu/info/20033/classical_studies/61/teacher_workshops
http://www.wyomingcatholiccollege.com/about-wcc/summer/conventiculum/index.aspx
http://classics.avemaria.edu/polis_greek_and_latin (near Naples, FL)
In Europe, there is:
http://www.lvpa.de/index.php (they haven’t posted place and dates for the summer seminar yet. In Poland, the Czech Republic, or Germany).
https://vivariumnovum.net/en/summer-school
(in Rome)
http://www.paideiainstitute.org/ (for high school students. In Italy and Greece)