If your students really resist answering questions orally, try having some sort of "exit pass" as a means of assessing student outcomes from the day's lessons. There are lots of forms this could take:
-You could have students list one thing they "really get", one thing they "somewhat understand", and one thing that is "still confusing" from the day's work.
-You could ask students to record in 10 words or less the main point developed in the day's activities (forces them to commit their knowledge to paper!)
-You could read a series of numbered statements and have them rate each statement by the corresponding number on their paper - 1 means completely true, 3 means completely false, 5 means unsure, whatever...
Reviewing such passes takes time but the concrete response is sometimes safer and more reliable. The key is getting students to understand the need to include their name on the paper and to see this as information for you, not a grade in the record by their name.