Purpose: The purpose of this letter is to clarify the psycholinguistic underpinnings of the tense marker total and tense agreement productivity score and to extend the discussion of when composite diversity and productivity measures are best used. Conclusion: We encourage the use of composite diversity and productivity measures when assessing grammar early in development, but we discourage the use of composite accuracy measures until children demonstrate emergence of diverse tense/agreement morphemes across a sufficient number of low-frequency sentence frames.