I don't know if you can import the mis data through a sql statement or in a database of some sorts. Because if you can, a matrix is easiest by doing a "cross join" of the same data. In this case you would join on student numbers and you would exclude similar test types in the join. E.g. you want to see Student A KS2 joined with Student A KS4 data.
In this Knowledge base article: http://kb.tableausoftware.com/articles/knowledgebase/market-basket-analysis the exact steps are described to create such an analysis that is commonly known as a market basket analysis.
I hope you can pull it off by creating such an analysis.