Arabic script is the earliest script taught to Muslim children around the world regardless of languages spoken at home. The script is sharp, crisp and clear. This makes reading of Arabic script very easy for very young children, most of whom can also memorise what they read, and for a lifetime.
The English alphabet & script is a sharp contrast to the Arabic alphabet & script, and many children fail to memorise the English alphabet and words of English till in their teenage years, when English is not the mother tongue. This slows down their learning of English considerably.
It will be good to try and teach the Arabic script first at home, then in pre-school, and later in formal school, and then introduce the English alphabet later. as well in first grade By the time Muslim children reach school age, most can read the Quran well, which is written in full Arabic script and without translation, but many cannot read any English text written with English alphabets.
Thus, if we want to test children's IQ for language proficiency, we have to test both their Arabic proficiency and Quran recitation, in addition to testing their English proficiency, and their mother tongue language(s). It will be unfair if Muslim children are just tested for English proficiency alone on IQ test when they also have a large reserved knowledge and proficiency of Quran recitation (proficiency) at the same time.
Most children who can read and write the Arabic script and read the Quran, will also be bilingual or multilingual. Whether the Arabic script stimulates or impresses on visual acuity and early brain development in very young children is yet to be discovered.