333 elementary exercises - single melodic line - can be used for rhythm practice, melodic practice, use of solfa, singing to note names, with an ostinato etc.
David Vinden's book "Songs for Singing and Musicianship Training" and his "Introduction to the Kodály Concept" both have a chapter called ""Making the most of the 333s of Kodály".
To be found under David Vinden (KCL) Publications - Musicianship.
See also "Teacher Handbook for Kodály’s 333 Reading Exercises" to be found under Reference.