Expressive Vocabulary Repertoire: Basis for Qualification?

I recently had a discussion with a colleague regarding qualification of speech therapy based solely on the number of expressive vocabulary words a child uses.

When working with very young children (under age 5), we understand the range of "typical development" can be very large.  So when I assess these children, I do want to have an accurate picture of the number of expressive vocabulary words a child uses. However I also want to take into account other things that will give me a holistic view of the child's expressive language skills.  So I ask myself (and the parents/guardians as necessary) these questions:

1. Does the child use language for a variety of social purposes (labeling, requesting objects, requesting actions, requesting assistance, greeting others, initiating/terminating activities, protesting, etc.)?
2. Does the child use various types of words (nouns, verbs, adjectives, greetings, negatives, etc.)?
3. Does the child combine words together into 2-3+ word phrases and create novel word combinations?
4. Does the child exhibit periods of time (3+ months) where he/she ceases to learn new words?
5. Does the child cease to use previously known and used words?

If I can answer "yes" to questions 1-3, than I am fairly confident this child is developing language naturally yet he/she may simply be on the low average end of the "typical range" when looking at expressive vocabulary repertoire.

However, if I answer "yes" to questions 4-5 than I cannot ignore that there may be some underlying issues affecting language development and will either recommend further assessment or suggest treatment if determined appropriate.

So, how much stock should we take in expressive vocabulary inventory?  We certainly should take some stock in it as it does give us a guide and starting point into understanding a child's expressive language skills.  However it alone is not adequate to determine the existence of a delay or disorder.  Therefore we must continue to take a holistic approach to assessment and we most certainly should be asking ourselves the above questions when analyzing our results and determining if further services are needed.

Happy talking!