Most (not all) college instruction is TIME based: they instruct you for a period of time, measure the results of your performance during that period of time, and at the end give you a grade that reflects the degree to which you mastered the material.
Almost all scuba instruction is instead PERFORMANCE based: they keep teaching you until you meet a standard of performance, at which time instruction will cease.
Absolutely correct... but it is worth noting that, in nearly every case, PERFORMANCE based scuba training is also linked with a minimum provision of training (classroom hours/water sessions/dives), which is stipulated by the agency providing the course structure.
Also, in most cases, those courses are advertised on the basis of that minimum provision of training. There is no explicit description of the protocol to be followed in the event that the student does not achieve the necessary standard of performance within the minimum/advertised duration of the course.
Some instructors/operations provide that explicit description as part of a 'learning agreement' - a contract which illustrates the performance-based nature of the course, sets out minimum training provision - and also explains what the student can expect should they not achieve the standards, within the timescale and training program agreed upon.
Some instructors/operations might choose to offer open-ended (INFINITE) courses, providing on-going training for as long as it takes the student to make the grade. This is essentially a 'guarantee' that you will achieve certification within a set COST, but flexible timescale and training provision. These are especially common in 'pro-level' courses... divemaster and instructor training. They are very rare in technical diving. They are probably around 50/50 in general recreational diving (whether formalized as learning agreements or just communicated to students as an afterthought, should the case arise).
Other instructors/operations might choose to offer FINITE duration courses, where any remedial training - to attain the necessary PERFORMANCE standards - is subject to a 'paid extension' of training. Thus, you are still assured of achieving certification, but not within a set COST or timescale. For recreational training, the vast majority of students might reasonably expect not to need such an extension - which is why most dive ops don't bother with spelling out their 'remedial training policy' in writing/contract. This expectation is not true for technical diving - hence the popularity of formal 'learning agreements' at that level.
With respect to this thread... lets be clear.... nobody FAILED the course. The participants simply didn't meet the performance standards within the set (minimum) timescale. Their progression in the course was suspended, pending remedial training to meet those performance standards. That is neither rare, nor exceptional, nor unethical.
What WOULD be unethical was if the students DID meet the performance standards - but were withheld from progressing anyway.
Other than making wild assumptions based on a stated a 'law of averages', there is NO WAY to determine what actually happened from the information provided thus far on the thread. We would need to hear from the instructor concerned (the other side of the story) and/or go into a LOT more detail with the OP about what skills they performed and what happened when they did those skills...
In reality, the training agency concerned (SSI) needs to investigate this, because only they will have access to the students, instructor and the training records for that course. It is THEIR job to ensure that instructors act ethically - and that students are both (1) meeting performance requirements and (2) not being delayed/costed when they do meet those requirements.
What I see as the lesson to be learned from this, is that Groupon-type deals need to be supplied with a clear 'Learning Agreement'... a formal contract which spells out exactly what a student's expectations might be - especially concerning the need for remedial training and course extensions... and the cost thereof.
It's usually done by instructors with lax standards who don't hold students up to par. If anyone can pass in 5 days, no worries about class time running long, it never runs long.
Which begs the question.... "what is normal?"
Is it normal for 99% of students to maintain 'mastery' of 20+ skills, psychological comfort, performance fluidity and the 'ability to repeat drills easily' (in-grained skill)....all within a very limited timescale, with a high student-instructor ratio...?
or
Is it normal for 99% of students to graduate from courses, 'conveniently' within the with
bare minimum stipulated training provisions?
Clue:
Look at how many posts/threads/comments we see here on Scubaboard that highlight the poor state of scuba diving skills... bad experiences with 'insta-buddies'... etc etc