Despite the relevance of agreement structures in constructing the interlanguage (IL) system of the L2 learner, not much research has been conducted in this area as far as Arabic language learners are concerned. This study investigated the acquisition of morphosyntactic agreement structures by Arabic as Foreign Language (AFL) learners in Ghana, using the Processability Theory (PT) formulated in Pienemann (1998, 2005). The data collected were analysed by using distributional analysis, a pre-defined emergence criterion and implicational scaling. The results of the study suggest that: (1) acquisition of agreement structures by AFL learners in Ghana seems to develop, generaly, according to PT's predictions; (2) there is enough evidence for the stability of developmental stages. In effect, that seems to confirm the cross-linguistic plausibility of the theory. The study highlights the importance of teaching L2 learners structures that they are cognitively and developmentally ready to process so that the entire teaching practice would be beneficial. Otherwise, learners IL development becomes stagnated, teaching becomes ineffective and precious classroom time is wasted, eventually.