A study investigated the disparity between the English-as-a-Second-Language (ESL) competence of South African black children and the competence required to comprehend content subject textbooks. Two ESL schemes and two fifth-year general science textbooks were analyzed for differences in vocabulary, syntax, speech acts, cohesion and coherence. Results indicated that: (1) there was a large jump between the vocabulary taught in the schemes and the vocabulary used in the texts; (2) the relative proportion of new vocabulary in the science lessons was very high; (3) the speech acts and their pragmatic force were similar across schemes and texts; (4) the textbooks used a much broader range of syntactic structures than the schemes; (5) the schemes used a much narrower range of cohesive devices than did the textbooks, and did not explicitly teach the use of cohesive or coherence devices; and (6) of the two textbooks, the one with by far the more difficult syntax also had a much more constructive use of cohesion and coherence conventions. Findings suggest that children should be introduced to the conventions of expository text in their English schemes, and that textbook writers should be made aware of the language limitations of their audience. (Three figures representing the design of the study and 16 tables of data are included; a list of 130 references, a further analysis of content subject textbooks, 4 textbook passages chosen for analysis, a visual demonstration of impact of unknown vocabulary, a trial computer run on 100 sentences, syntactic structures and elements in textbook passages, and passages from the English schemes are attached.) (RS)