I can't speak to the online law schools, but MCL, who started this thread, and is a residential program, has had the following policies. There is no required curve. Students must maintain a minimum cumulative GPA of 70.0 (CGPA) or better to remain academically eligible to remain in the JD program. Students on academic probation must bring their CGPA up to 70 or higher within one year. Students who fail to do so may elect to transfer to the Master of Legal Studies Program and receive their Masters upon completion of 36 units. Students on academic probation are assigned individual tutors and provided supplemental resources, academic counseling, and strict monitoring during their probationary term. Students on academic probation who scored lower than 65 in a bar-tested course are required to repeat the course (but no additional tuition is charged). The higher grade is counted towards the CGPA.
The result has been the following (on average). Out of 35 1Ls, 6 will fail to meet the 70 CGPA. 2 of these will be substantially below (65 or below) and will repeat first year with tutoring (no additional tuition charged), 2 will repeat one class with tutoring, resulting in a reduced 2L class load while they repat the 1L course, and 2 will opt to go the route of the MLS degree. We rarely have anyone completely quit at the end of 1L.
We do have other, non-academic attrition for work, finance, health, relocation, etc. over the four-year, part-time program. We anticipate that, on average, out of the original 35 1Ls - 25-27 will complete their JD, 3-5 will complete the Masters, and 5 will not complete either program.
For the 25-27 JD graduates, 3-5 will never take the bar exam (JD degree for other business reasons) and the remaining graduates will achieve an appx. 65% cumulative bar pass rate on the California Bar Exam. (With some recent classes achieving as high as 70%). Our statistics (that are openly shared with the students), indicate a direct correlation between law school graduating GPA and bar pass results. Although a 70 CGPA is required to graduate with the JD, our statistics indicate that a 73 or above is necessary to have a reasonable chance of passing the CA bar exam. Therefore, those graduating with GPAs below 73 have full knowledge that they have a very low prospect for ever passing the bar, but they have been counseled to this effect at the end of every Spring Semester and provided the opportunity to transfer to the MLS degree program. Obviously, with an average 30-35% fail rate on the bar exam, there remain students who choose to complete the degree program (for many reasons), even though they have been provided information about the relationship between their academic GPA and bar passage.
As a small "opportunity law school" the above model fits our community and is perceived as being very successful. It is difficult to compare our program to the typical ABA model, but we believe (for the past 43 years) that it has many positive aspects as a result.