I was part of a Year 6 classroom this past week and noted how the teacher was working in an interdisciplinary manner. On the day of my visit the children were engaging in extended writing, drawing upon imagery and symbolism from their current topic. Their work was bounded by the rigours of English, a subject of the school curriculum. Their focus was on writing, the expression of thought and feeling through writing using the conventions of writing.
Learning through their topic, WW2, was embracing an interdisciplinary approach. In History there was study of the period 1936-1944 in England, and in Literature the reading of C. S. Lewis’s Narnia and Anne Frank’s Diary, and in Art images from the Blitz had been transfigured through the children’s artistic imaginations. So, you see how their learning was ‘involving two or more academic, scientific, or artistic disciplines.’ 
The teacher was making a clear distinction between extended writing in English and extended writing in History. Historical writing called specifically upon historical knowledge and skill. The children’s study of English, Art and History had depth.
But what was of particular interest was that this learning involving two or more disciplines was yielding an unplanned conversation. The children were asking questions, wanting to understand more, relating what they were learning to their present circumstances. Class discussions were becoming ever more important to the children.
Interdisciplinarity is a gift to the primary school teacher. Unlike the secondary school teacher, the children are with their primary teacher a good part of the time. The whole curriculum is their oyster. In this case it would seem that there is rich-learning in progress, that there is powerful knowledge being engaged with.
Ah! wait a moment because the term powerful knowledge lies within the fiefdom of particular parties and is to be understood in a particular way. I was using it casually.
There is in the promotions of powerful knowledge an insistence upon the integrity of subjects and their rootedness in what is referred to as disciplinary knowledge. And that this integrity demands depth through a lengthty induction into the subject’s character, its conceptual structure and body of knowledge. It is only when a worthy level of mastery of this is reached that interdisciplinarity is countenanced.
John White challenges the powerful knowledge thesis and makes reference to the question of interdisciplinarity. Do focus on this if you can.
In general, attempts to achieve interdiscipinarity in our schooling have not been good. Superfical relationships between subjects are made, a scraping of the surface to find connections and then the terrible case of the Blues in year 8 where the hapless music teacher serves up a reductive version of history leading to the History teacher raising their eyebrows.
an example of music in interdisciplinary relationships and no raised eyebrows.
It is this kind of interdiscipilnarity that leads to a conversation where minds are opened, questions raised and, for a child, their becoming a part of a wider conversation. It is a time when
‘…teaching and learning allow us to forget for a while to be preoccupied with ulterior goals and purposes that [schools] fulfil the peculiarly human desire for self-understanding which give rise to them.’ 
 Webster Merriam Dictionary Timothy Fuller (1989) in the
 Introduction to The Voice of Liberal Learning, (1989) Michael Oakshott. Liberty Fund. Page xix.