Recent curriculum intrusion in the U.K. through the work of the Literacy and Numeracy Task Forces have drawn attention once more to the importance of 'expert' teachers working in classrooms alongside their colleagues. This was a major focus of work during the 1980s when a large 'army' of advisory teachers was established to work alongside teachers in their classroom in revising the mathematics and science curricula. Appraisal of that work indicated a number of factors which need to be taken into account in such developments including the need for contracting and working agreements on anticipated outcomes and acceptable intrusions, supportive out-of-class working, whole school involvement, insider/outsider perspectives and the establishment of 'credibility'. The new proposals include reappraisal of the role of curriculum consultants, and on some interpretations of the use of the newly identified 'advanced teacher' grade. This paper examines some of the issues that arise when such in-class support work is initiated.