Dear Clay,
At the moment, I am carrying out a research on designing courses for multilevel groups. This requires a lot of testing for students' independent work according to lacks and needs. So, I think that as many teachers as possible could work in integrating data banks per level, so that, whenever it is needed we could create assessments or evaluations either by selecting items per skill, language system, and levels, or by randomly designing them.
To solve the problem of levels, we could first use the Common European Framework of Reference for Languages: learning, teaching assessment (CEFR, http://www.coe.int/t/dg4/linguistic/Cadre1_en.asp). We could also split each of the six levels in two or three parts, as agreed according to needs, or use the levels of English defined in the Core Inventory for General English ( http://englishagenda.britishcouncil.org/publications/british-council-eaquals-core-inventory-general-english ).
If interested, please get in touch.