There are a number of assessment tools that can be used for assessing pupils at an early stage of English or for those that have English as a second language.
NASSEA has produced a very useful publication that is being used by many Local Authorities and schools who wish to assess initial levels and progress of EAL pupils.
The National Strategies have also produced some interesting assessment models and processes. This booklet is the latest from QCA relating to Assessment of EAL pupils.
http://www.standards.dfes.gov.uk/ethnicminorities/resources/markingprogress.pdf