Obvious barriers to learning are barriers of a physical nature, or the ones created by the attitude of others: the trip to college/school may be a lengthy one, or it might be dangerous to come back home late at night because the area is unsafe; there might be financial constraints; the course's content is badly presented and the teaching poor; family members might not approve and might not be supportive; childcare provision is expensive or non-existent.
A student needs above all motivation to pursue and continue her/his studies, and all the above can be fatal 'barriers' to learning: they are issues of a practical nature, and they are very real. There are though other more insidious barriers: the ones we create internally. Unfortunately these are a bit more difficult for a teacher to identify, and people are often very much caught up in this kind of attitude: there is a lot one can do to help though, as I will explain shortly.
Internal barriers may be of a psychological nature (lack of interest, worry, lack of confidence); may be originate from a negative past experience (stereotyping, dislike of a particular learning method, preconceptions); or they may be due to fear of change and personal reasons (dislike of the teacher and course structure etc.). Of course internal barriers are much more difficult to identify, as they are not always clear even to the learners themselves: but if the teacher is providing a healthy social environment, and if the learners become aware and willing to challenge their preconceptions/beliefs, internal attitudes can indeed be changed for the better, resulting in a happier learner and overall happier individual.
Internal barriers are often rooted in the academic self-concept of the learner and their self-esteem. I am not saying with this that it's the 'learner's fault': after all, if such barriers are there, it's because something unpleasant has happened, or there was never the opportunity to go beyond a certain belief/attitude due to environmental factors. I am saying though, that if an internal barrier is there, it can be removed. How? It's about internal 'homeostasis'. An attitude is supported by three factors: belief, feeling and action. Together these three components make up the attitude, which may be positive or negative: all the components will fit with each other.
Belief: the subject is too difficult, I cannot simply grasp the basics and progress
Feeling: I become very anxious any time I am given an assignment
Action: avoidance, passivity
There is indeed a balance, as belief, feeling and action are all coherent and paint a uniform picture. If though, a teacher presents the learner with a methodology that resonates with the learner's personality, and the student starts making good progress, their belief will change accordingly to what experience shows to be true: the subject is not too difficult after all, and can be learnt. Therefore, the learner will become much less anxious, and will actually come to enjoy the subject: hence avoidance will stop, and it will turn into active participation. So the final result will be:
Belief: I understand the subject and I am making progress
Feeling: I feel good with my progress and I feel well when I study the subject
Action: active participation, effort
As young or mature adult learners, I think it's very important to do some self-assessment here and then, and check that what we believe to be true is not in fact a construct of our underlying fears: we do create barriers for ourselves for example when we are scared of being seen as incompetent or foolish. It's in fact possible to attain positive change, and it's not at all difficult: it just takes a little bit of patience, effort and self-awareness.