Speech and language therapist and teacher practitioners need particular knowledge to work effectively together to support the needs of individual learners. Using the frame of modes of knowledge (Gibbon, Limoges, Nowotny, Schwartzmann, Scott, and Trow, "The new production of knowledge", London, Sage Publications, 1994), the necessary knowledge bases in the current Scottish policy context are analysed. It is argued that a fresh approach is needed which investigates the kinds of specific practitioner knowledge needed to support a pupil with specific language impairment. Empirical data from one collaborative support context are analysed to demonstrate how practitioners' knowledge bases are manifested. The analysis suggests that practitioners and their managers and leaders will be better placed to audit how and when different modes of knowledge are needed in the cycle of their co-work, to identify any gaps or overlaps in the types of knowledge necessary and to ensure that these are addressed in future in practitioners' pre- and post-qualifying professional education and learning. (Contains 2 figures.)