Challenges of teaching Biochemistry to Health Sciences students

Had anyone told me, 20 years ago, that I would earn my living as a lecturer, I would have considered it as a put-down. I did have a lot of respect and appreciation for (most of) my lecturers at the University of Porto, but I expected to become a full-time scientist, rather than a "lecturer who finds time to do some science in-between classes/grading" or a "researcher with required part-time lecturing duties". Real life disabused me of that expectation: due to the dearth of other scientific jobs in Portugal, I did become a "lecturer who finds time to do some science in-between classes/grading" after finishing my PhD. 

The culture shock I experienced when I first lectured to Health Science Students left me unable to speak about much more than the woes  of teaching for the best part of a year. A big portion of my surprise came from my first-contact with regular students who attended my lectures simply because they were required to by the University, rather than due to recognizing the subject as a relevant background for their (mostly) vocational training as Physical Therapists, etc. Being required to take most classes to graduate  (rather than choosing large part of the curriculum around a core subset) is a very common feature of university curricula in Portugal. In principle, it is meant to ensure that all students have a balanced curriculum and do not "flee" the hardest subjects. In practice, it also tends to lead to ever larger classes of those same "hard subjects", since students tend to consider those lectures as bureaucratic hurdles thrown at them, rather than as valuable knowledge and therefore feel disengaged, alienated and fail them in large numbers.

All classes I have taught (Biochemisty, Organic/General/Analytic Chemistry, Basic Mathematics/Statistics) fall into the "hard subjects" class. In my first years of lecturing, I had a most demotivated cohort of students. My expectations regarding their performance were generally very unrealistic, as my baseline comparison was my own student experience at my "alma mater", where I was surrounded by engaged student peers who were motivated into learning pure scientific subjects, and did not regard them as "filler" or "bureacratic hurdles" aimed at winnowing the sutdent body. Moreover, my "alma mater", the Faculty of Sciences at the University of Porto, was famous among students by its harsh grades: attrition was relatively high, less than 20% of those graduating from its Chemistry or Biochemistry curricula would have an average grade of 16/20 or 17/20, and higher final grades were virtually unheard of. In other Portuguese Universities, final average grades of 18/20 were common, even though their student body was of the same (or even slighly lower) quality, as judged by their entry grades.

I eventually adapted to the students' expectations, and developed a teaching method that engages students and apparently motivates them (as judged from the appreciative comments in teacher evaluation forms). However, I find that this only seems to work during class time: students pay attention, seem to be making all the right connections (as long as I softly nudge them towards the right path, etc.), congratulate me on the quality of lectures, etc. In tests/quizzes/exams, however, a strong disconnect appears: ca. 50% of my students still struggle with many concepts that I would consider as absolutely basic. Why does this happen?

I have just found out that there is a proper name to what is happening in my classes: pseudoteaching (defined as " The concept [...] that even the most outwardly perfect lesson can result in students not actually getting what it is you wanted them to understand."): along with this, there is also pseudolearning ("Going through the “expected” steps without extracting a solid, working understanding of a topic would") and pseudostudying (which I would define as "reading and working the material to the point where one feels tired  but without actually taking anything from the exercise due to inability to distill the core concepts into working knowledge").  I cannot prevent students from pseudolearning or pseudostudying (apart from exhorting them to rest properly, keep their blood sugar levels up while studying and work/study in short bursts daily rather than pulling all-nighters on the eve of the tests). Avoiding pseudoteaching is in my power, but I do not (yet) know how to: Jan Jensen (following Mazur) advocates a flipped classroom model where exposition occurs outside class time (using short video lectures and key exercises) followed by solving exercises "in-class" with free exchange of ideas among students (peer-instruction). I do not think this  method would help with my students, though: a previous experience of short (< 10 minutes) in-class quizzes led to class disruption, acutely stressed students during and after the quiz and minimal improvement in weekly off-class engagement with the study material. What would you suggest me do?