In English

The Arabic writing system is an alphabetic system with twenty eight basic consonant letters. Most of these consonants show a very close resemblance in form, with only additional dots or strokes to distinguish them from each other.  They are usually composed of one base form and most of them have up to three or four distinct variant shapes.  Graphemic variants differ depending on whether they occur independently (non-connectors) or in word initial, mid- or final position.  The Arabic orthographic system is characterized by a plurality of letters (more than sixty base forms), which stems from the cursive nature of the Arabic script and its ample use of ligatures and letter combinations.  The use of multiple letter forms leads to graphemic difficulty and becomes a significant learning problem and a considerable burden for the Arabic text decoding process,which is vital for the acquisition of basic literacy skills.   
The Arabic script uses diacritical forms (or diacritics) for vocalic representation (a, i, u).  Four letters (‘alif or‘imaala, waaw, yaa’) are also used to represent vocalic length.  One diacritical marking, the shadda, is used for lexical differentiation.  Most of the grammatical functions at both the morphological and syntactic levels are represented by the short vowels, which also represent mood and case endings in the Verb-Subject-Object fusha syntax.  Thus, vocalic representation carries the weight of the whole grammatical system and is therefore extremely important in setting up functions leading to correct reading and acceptable text understanding. However, these short vowels are rarely present in everyday out-of-school writing, and they do not, as a rule, appear in most printed materials in the Arab region. 
Diacritical markings are rarely used in printed documents and this generalized practice includes the shaddah (consonantal length) and the hamzah (glottal stop) also.
The use of diacritics, which is restricted to primary school education and the sacred Koranic text, seems to be limited to whatever length of time is considered sufficient for the learner to be initiated to reading without them, which generally amounts to between four and six years.
Nowadays, vocalized Arabic text seems to be only used in pure deference to the needs of young and inexperienced learners.  In order to be able to read, everybody, even inexperienced neo- and  low-literates, has to provide his/her own grammatical interpretations and brings to task considerable additional knowledge of syntax, vocabulary, and sometimes contextual interpretation in order to obtain correct and meaningful
vocalizations which will allow them to reach acceptable word recognition and sense disambiguation.
Because the Arabic reader needs to understand in order to read, the Arabic reading process seems to have completely reversed what is usually the norm in other languages, where people read in order to understand....