(1) Every student has his or her point of challenge. If I have done my job and pushed each student to their own point of challenge, and check in with them frequently enough to assess their progress, there is no question that each student can learn. The solution to this is to have a very interactive relationship with students.
(2) Yes, all students can learn. The key to ensuring this is to find what works best for the individual learner. Finding out how the student learns best, i.e. what type of memory he or she has: kinesthetic, auditory or visual memory. The next step is to find each student’s interests and relate the concept being taught to their interests.