Nowadays, in many European countries people from all over the world work and live. Consequently, schools are multicultural and multi-linguistic and pupils that are not proficient in the language that supports learning and assessment are clearly in disadvantage when compared with those of highly proficiency in the official school language. Besides, the promotion of scientific literacy is actually an issue of major concern of the science education community, being “(…) an aspiration for most, if not all countries” (Gilbert, 2004, p. 7). Among other reasons, this concerned is based on the belief shared by policy-makers world-wide that economic grow is dependent on the scientific and technological capabilities of the labour force (Drori, 2004). In the last twenty years, international comparative studies, such as TIMSS and PISA emerged, enlightening the student achievement in aspects related with scientific literacy and proficiency in official school language. The findings and conclusions of these studies have been largely debated and have had important consequences and impact, namely in the teaching practices and in the teaching syllabuses. Portugal was classified in a very poor position in the league tables regarding science and scientific literacy in all international studies. Moreover, according to the Ministry of Education (2006), Portuguese schools are attended by pupils from 120 different nationalities, speaking at home 80 different languages. We can wonder if a weak performance in a written scientific literacy test cannot be due to their poor understanding of what is demanded. Consequently, the scientific literacy level of the pupils being assessed may be masked. Therefore, a research study was conducted aiming to clarify if and in what direction and extent pupils’ proficiency in the official school language influences pupils’ assessment of scientific literacy.

The research follows an ex post facto design in a causal comparative model. A cross-national sample was constituted following a stratified group model and is constituted by 1156 pupils of the 9th grade pertaining to 60 classes from 21 different schools. Pupils' proficiency in the official school language is indirectly assessed using as indicators the language spoken at home, the pupils’ nationality, the country where they were born and pupils grades in Portuguese language. Three groups were constituted. One constituted by the pupils that were born in Portugal and speak Portuguese at home; another constituted by the pupils that were born in Portugal, but speak at home a foreign language and, a third constituted by pupils that were born in a foreign country and speak at home a foreign language. A pilot study was conducted to address the validity and reliability of a set of activities intended to assess pupils’ scientific literacy, previously selected from the PISA science units. The opinions and comments of ten university experts in several scientific areas and in education were also taken into account in the validity process. At the end, a set of written activities adapted from the former ones were used to assess scientific literacy. The statistic software SPSS 15.0 is being used in the analysis, using a multivariate model with specific effects of explanatory variables. Also, a content analysis of the pupils’ answers to the activities performed by ALCEST is underdevelopment in order to identify the nature and frequency of the difficulties pupils have when answering the questions.

The content analysis of the pupils’ answers to the activities reveals the nature of the main difficulties that pupils’ have when answering the questions. The data gathered can be used in order to find an effective way to promote a scientific literacy for all and yet, when planning scientific literacy assessment. The findings can help to shape the educational policies and, in particular, can raise the awareness of the science education community, mainly teachers, for the importance of taking into account pupils’ background diversity, especially the cultural and the linguistic diversity, when conceiving and developing materials intended to enhance or to assess pupil’s scientific literacy. The variety of data that were collected allow also the explore pupils’ intention to continue studying, pupils’ motivation to read and the nature of what they read, pupils’ backgrounds and the professions that pupils expect to embrace are predictors of pupils’ scientific literacy. At last, being the assessment of scientific literacy influenced by the proficiency in the official school language, further research is needed about how to conceive and implement the assessment of the scientific literacy in national or international studies in order to overcome this challenge.