The general aim of the thesis is to show how The Situational Language Intervention Programme (SLIP) was formulated in order to include the critical factors of: the cognitive abilities and linguistic characteristics of the intellectually handicapped; pragmatics, semantics and syntax and the four models of language acquisition; the criteria that guide language intervention programme development; the use of precise and systematic teaching methods that stimulate the use of language in the students' environment. The general objective of both SLIP and this thesis is to show how to increase moderately to severely intellectually handicapped adolescents' language-communication through the appropriate use of the forms of language applied to its functions in a specific range of situations. Chapter Two of the thesis is concerned with the cognitive abilities of intellectually handicapped people and the implications of intellectual handicap on communication and language development. In addition it discusses, stage by stage, the positive and negative markers of language acquisition. These markers illustrate to the teacher the signs of linguistic retardation at each stage of language learning. The contents of Chapter Three provide an outline of the four models of language acquisition, i.e. Pragmatic, Semantic/Cognitive, Psycholinguistic/Syntactic and Behavioural. Those models contribute to our understanding of how language develops and illustrate to us the complex nature of language acquisition. In addition, this discussion documents the past and current research viewpoints and draws our attention to the limitations that existing theories have in providing a "full�blown" model of language acquisition. Furthermore, Chapter Three is stating that the recent analysis of language-training for communication disordered and intellectually handicapped students has shown that a more balanced study of the semantic and pragmatic factors in language acquisition is emerging. This chapter is urging teachers to re-analyze, re-evaluate and modify their language intervention programmes by integrating the syntactic, semantic and pragmatic factors. Both the contents of Chapters Two and Three are demonstrating that it is necessary to address the theoretical viewpoint and academic findings both of which are important aspects of the role of the interventionist. They have to be addressed if the teacher is to make judgments concerning the efficacy of different models in attaining certain goals. Such factors govern the utilization and integration of certain approaches and procedures. The contents of Chapters Four and Five discuss how the language interventionist can lead the intellectually handicapped student into increased language usage and communicative competence. Chapter Four is concerned with the current critical issues and developments in: curriculum and programme design for the moderately/severely intellectually handicapped adolescent; criteria to guide programme development and direction of language intervention; direct instruction techniques; augmentative communication systems and their basic programme guidelines. Chapter Five outlines the framework of the Situational Language Intervention Programme (SLIP) which was designed and implemented by the author. The content and procedures utilized by SLIP are greatly influenced by the contents of Chapters Two, Three and Four. This influence is demonstrated in the discussion concerning SLIP's: aims and objectives; content and design decisions; selection of forms to be taught; sequencing; teaching procedures and methods of instruction. Chapter Five also discusses the implementation of SLIP.