In the course of inclusion, migration and flight, German schools are experiencing a heterogeneous student body concerning language competences. Many students have difficulties understanding schoolbook texts in scientific subjects (OECD, 2016). Especially biology schoolbook texts offer barriers to comprehensibility, which can occur in various forms, such as a high number of technical terms, subordinate clauses and compounds (Schmellentin et al., 2017).

Parallel to this circumstance in biology, the concept of Plain Language is becoming prominent in society. Plain Language is a variety of language that follows certain principles such as the avoidance of subordinate clauses and segmentation of compounds for facilitated reading and comprehension (Maaß, 2015). It is aimed at people who do not (fully) understand standard texts, as for example people with a learning disability or migration background (Maaß, 2015). In the course of inclusion, the concept is being discussed for the use in schools. So far, research has been limited to the use of Plain Language in different subjects, but not biology.

The project has already identified parallels between the characteristics of Plain Language and possible text barriers in schoolbook texts of biology. When such a text is modified according to the rules of Plain Language,  numerous possible text barriers can be lowered, which may result in the increasement of comprehensibility.

Regarding the presented context, testing of the following hypothesis was of interest: After an intervention in biology lessons with the use of schoolbook texts in Plain Language, students achieve a significantly higher increase in reproductive knowledge of the subject matter covered than students with schoolbook texts in original language. Concerning the attitudes of the main stakeholders, explorative questions were developed such as ‘How do students rate certain rules of Plain Language, such as the segmentation of compounds?’.

The study follows a pre-post-test design with the use of mixed methods. At the beginning, the learners were confronted with a C-test, which determines the general language competence level of the students. Before and after the intervention, the learners were given a knowledge test with open items on the content of the intervention. Furthermore, a questionnaire on the learners' attitudes towards Plain Language with both open and closed items was given. The teaching intervention consists of six lessons with schoolbook texts in Plain (within experimental groups) or in original language (within control groups). In order to determine the teachers' attitudes towards the use of Plain Language, interviews were conducted. In addition, the teachers recorded observations of students' comments on the texts during the intervention. The qualitative data will be analysed with the help of qualitative content analysis. With regard to the knowledge test, the increase in knowledge is calculated from the difference between the results of the pre- and post-test. The comparison of the knowledge tests is carried out with the help of statistical procedures such as the Kolmogorov-Smirnov-, Mann-Whitney-U- and Kruskal-Wallis-H-test for the main and sub groups of ‘non-existing’, ‘existing’ or ‘possibly existing need for language support’ as evaluated by the C-test. The sample selected for the pre-study consisted of 100 fifth graders and five teachers from secondary schools in Germany.

Results from the pre-study show a significant increase in the reproductive knowledge in all (sub-)groups, except for the subgroup ‘possibly existing language support’ within the control group (n = 3). However, there could not be found a significant difference in the comparison of knowledge growth between the experimental (n = 61) and control group (n = 39) (p = .110, r = -.16, z = -1.599) and subgroups (p = .108, d = .423, H = 9.023). A first evaluation of learners' attitudes towards Plain Language texts in biology lessons show that some features of them were rated positively (e.g. short sentences and large font) and some negatively (e.g. the segmentation of compound words) by all students (n = 100). Furthermore, the findings show that learners with (possibly) existent need for language support (n = 31) rate Plain Language more positively after an intervention with it than learners without any support needs (n = 30). The impression is that the use of Plain Language texts in biology lessons has no influence on the declarative knowledge. The Cognitive load imposed by the different texts may be similarly high for both variants (Härtig, 2019). Still, the results seem to suggest that students, especially with (possibly) need for language support, prefer schoolbook texts in Plain Language. This may justify the use of them as it may have a positive influence on the motivation which may result in better academic performance after all (Deci & Ryan, 1993). An advanced analysis of the concept of Plain Language, also evaluating the teacher’s perspectives as planned within the study, could show whether the implementation of the concept into future schoolbooks could be reasonable. The results can also be of use regarding international concepts of Plain Language within the school context, as texts for biological education bare barriers to comprehensibility also in other languages (e.g. Fang, 2007).

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