Ethinx, your DC is actually too young for the TOWL. I would suggest the OWLS-II (Oral and Written Language Scales) instead, or the PAL-II (Process Assessment of the Learner - Reading & Writing). If both the written and oral portions of the OWLS are given, that will also give you some information on how much is language per se, and how much is specific to writing.
For pure expressive language, the slp may also choose to give the CELF-5 (this tests oral language only). The auditory processing (I assume) eval he's undergoing will not assess expressive language (though it may find other notable features).
