Here it is attempted to present a platform environment that allows development of various educational applications fully accessible by deaf users. Subject to Design for All primes, the environment is built on methodological principles which adopt sign language as the basic means for communication of linguistically uttered educational content. It also makes extensive use of visual objects to support comprehension and navigation at all levels of human-computer interaction. Currently available instantiations of the environment have incorporated both video for content presentation and an avatar based dynamic sign synthesis mechanism. The educational applications to be referred to when discussing the design principles and user requirements taken into account, include one web-based and one off-line GSL teaching tool for the same school level (early primary school) as well as a vocational training tool for adult users.