During the lecture on Lesson 7, you mention that the substitution exercise in 2b is a meaningful practice, because requires students to understand before they answer. I see that it requires the student's knowledge to answer the question, but I'm having difficulty in seeing how it is meaningful in helping understanding the presented structure.

To elaborate, the question "You want to see a film" tests the students knowledge on the word 'film' and its relationship to 'cinema' rather than the structure, "Is there a ... near here?"
The same follows for single-word prompt exercise 3b: it tests the student's understanding on the single-word prompts to answer "why?", rather than the application of the structure, "I'm going to ...". 

Am I misunderstanding the concept of 'Meaningful Practice' here? It seems that the relationship between meaningful practices and the practice of the structure is rather weak. The title of the lesson is 'practicing structures' and mechanical practice seems to focus on getting the students used to the structure, so I am assuming that meaningful practice should focus on testing the student's understanding of the presented structure rather than the words given by the instructor.