Yaqoub - I personally don't think that academic writing is a difficult skill to teach. It is a logical process and can be taught as a 'here are the key, sequential stages to follow'. Once the process is learned, students mainly need to remember and retain the skill over and over again. The problem for many students is two-fold. One - if they are taught different conventions by different teachers and, the main one, is that academic writing is not a 'natural' skill and is often 'divorced' from actual practice i.e. nurses do not need to write and deliver academic assignments when they are caring for patients.
Yaqoub, teaching academic writing is not, in my opinion, the most difficult skill to teach. One main challenge in teaching academic writing skills is emphasizing the need to learn this skill. Most students seem to see it as an unnecessary burden, and seem reluctant to take on lecturers feedback which -in their own words- they see as 'picky' or 'tedious'. Once students see the benefits of having sound academic writing skills, that goes hand-in-hand with advanced thinking capacity, they very quickly learn how to do it, and improve rapidly.
Yaquob yes it is difficult but depends on situation if someone write in their mother tong is very easy as compare to in second language for example in pakistan it is very difficult to learn writing in second language because we use three to four language it a time mother ton Pashto,religious activities in Arabic language, news paper and other curriculum etc in English and urdu