This study aims to investigate possible factors contributing to subject-verb agreement errors in Swedish junior and senior high school students' English written production. The sample data is collected from the Swedish Learner English Corpus (SLEC), which comprises student texts produced in a classroom setting. The texts are randomly chosen but evenly distributed in terms of binary gender, school year, and type of high school program. In this study, the texts included in the scope are written by students attending a Swedish-speaking school with Swedish as their first language. Errors are classified as overgeneralization or transfer and further classified in relation to the subject type, the verb type, and the distance between the subject and the verb. The classification of all correct instances of subject-verb agreement is also performed to further investigate possible error explanations. A total of 41 agreement errors were found in 24 texts written by students in the 9th and 11th grades. The results show that overgeneralization is more frequent than transfer errors. Overgeneralization suggests that the students are aware of the third-singular form but do not always apply it correctly, while transfer errors show a potential lack of awareness or attention to the form. In both cases, the errors indicate that these students have not automatized the principle yet. Errors are often related to subject types “a pronoun” or “a noun/noun phrase" and the verb be, which is the most frequently used verb. Most of the errors occur when the subject and the verb are in immediate contact, and more than half of them involve a relative pronoun as subject, which indicates that the learners have misinterpreted the grammatical principle or have not fully acquired it. Overuse of the third-person singular form can also be an effect of teaching and explicit learning, which makes learners apply the form whenever it seems possible and relevant.

The aim of the study is to find out to what extent Swedish learners of English, in the first year of upper secondary school, make prepositional errors in their written production, and to what extent these errors can be attributed to negative transfer, overgeneralization and simplification by conducting an Error Analysis. A comparison between gender and type of program, academic and vocational, is made to find out in which type of program most errors appear and if there is any difference in terms of gender.  The data is annotated from the Swedish Learner English Corpus (SLEC), which consists of argumentative essays written by Swedish learners of English, and it consists of 24 randomly selected texts based on the variables binary gender, type of program, Swedish as their L1, school year, and English course. All the texts selected are written by students in the first year of upper secondary school studying the course English 5. The results of the study reveal that Swedish learners of English struggle with prepositional usage. In total, 649 prepositions were identified in the 24 texts. Out of these, 72 (11.09%) were used incorrectly. The most frequently used prepositions involved in these errors are of, for, in, to, and with. Most errors appear when prepositional phrases function as post-modifiers in noun phrases. Substitution is, by far, the most common type of error found, meaning that the students replace the correct preposition with an incorrect one. The results thus show that the students seem to be aware that a preposition should be used although they fail to choose the correct one. Female students make more prepositional errors than male students; similarly, students attending vocational programs make more prepositional errors than students attending academic programs. Most errors are cases of overgeneralizations, followed by negative transfer from Swedish, and simplification. However, many of the errors can still be attributed to negative transfer which suggests that, even though Swedish and English are similar languages which could lead to positive transfer, this does not seem to fully apply to prepositions.