Here is a list of books, articles, blogposts that tackle the tricky matter of how to manage and teach MIXED LEVEL CLASSES!
PS – IF YOU KNOW OTHER USEFUL SOURCES, PLEASE, DO SHARE IN THE COMMENT SECTION!
Hess, N. 2001. Teaching Large Multilevel Classes. CUP
Prodromou, L. and Clandfield, L. 2007. Dealing with Difficulties. Peaslake: Delta Publishing – a bunch of possible activities to use in mixed-level classes
Articles / blogposts
Practical tips from British Council website. Will give you some more links to discover!
A chat summary on mixed levels. I found it VERY useful!
Classroom as a learning centre. Naomi Epstein gives a brief overview on how she manages classes of very mixed level deaf or hard of hearing students.