Rubrics and other measures for Assessing Rethink Literacy Skill...
If your school does not yet have a formal assessment for ELL students there are many alternatives. TESOL and Reading A-Z websites have all kinds of information and assessments and benchmarks pertaining to ELL students http://www.tesol.org/
Reading A-Z: https://www.readinga-z.com/ell/ell-assessments/
Referring to the Common Core State Standards is also another great resource for assessments and benchmarks for ELL students in regards to language and technology.