Background. The ability to formulate presenting problems in psychotherapy is widely acknowledged, but little is known about the skills involved. Treatment manuals are necessarily directed to the general form of a problem and need to be invidualised to the specific needs and circumstance of someone seeking treatment through formulation. The individual case formulation (ICF) approach is based on the functional analysis tradition within behavior therapy but aims to employ clinical descriptions that are theory-free. Formulations are depicted in diagrams constructed according to a set of basic conventions. Aims. Following on previous preparatory studies, the present paper reports on a test of whether this method of analysis and representation could be taught and if the quality of the resulting diagrams could be reliably rated. Method. Participants (N = 40) participated in a training course in formulation for posttraumatic stress disorder that was either self administered or presented live online. Results. A draft rating scale was refined in the course of rating the resulting formulation diagrams and basic inter-rater reliability established, despite a relatively high rate of formulations that did not meet minimal standards. Exploratory analyses examined the relation of derived scores to participant professional characteristics. Discussion. Results of the study support further development of the ICF approach.