Text coherence can be marked linguistically by using connectives and lexical signals that make coherence relations explicit. This study focuses on the influence of such markers on text comprehension in ecologically valid contexts. A first experiment shows how readers in a business meeting and in a laboratory study benefit from the explicit marking of coherence relations. A second experiment shows how poor readers in secondary education benefit from coherence marking while answering text comprehension questions. This paper argues in favor of an interaction between cognitively oriented research on discourse representation and document design research, to solve crucial questions like: how do we design optimally readable texts?