This research note presents partial results of a user test assessing the “communicative effectiveness” (Clerc & Beaudet, 2008) of a written communication aimed at citizens penalized for driving under the influence. The doctoral candidate is interested in the users interaction with an informational ecosystem composed of multiple sources of information. She compares the effectiveness of three ecosystems by checking their effects on users' comprehension, appreciation, and mental workload. These objectives require expanding the usual scope of the “communicative effectiveness” concept and exploring aspects related to reading/using multiple texts in an administrative context. The tests were conducted with 15 French-speaking adults without a high school diploma. An adapted version of the NASA-TLX questionnaire (Hart & Staveland, 1988) was used to measure mental workload. The data suggest that when faced with a letter of a high informational density, users with low literacy levels focus their attention on peripheral details at the expense of the main ideas. No correlation was observed between comprehension and mental workload. The data are now considered a "pre-test" used to refine the research design for a second wave of interviews.