Lately most investigations regarding Swedish students’ level in Spanish as a foreign language indicate that there is a notable gap in their linguistic knowledge. It is possible to give various explanations to this tendency, such as the capacity of the educators or the level of motivation the students have. These explications, however, does not explain the fact that this is a problem on a national level. In order to be part of the search to find a potential solution to this issue this investigation has been made with the intention of assessing whether the students truly learn what they are being taught, by means of a modified error analysis, in which there it has also been investigated what part of the Spanish language that seems to be the most problematic to learn for the students at a Swedish upper secondary school. Last but not least this study also attempts to look into the possible influences of the first language and the gender of the learners. The error analysis that has been used consists in a test that contains twelve sentences, of which six are incorrect. All the sentences were based on constituents of the Spanish language that had already been studied in class. The students who participated in this study, all of them at the first, third and fourth level in the curriculum established by Swedish National Agency for Education, where asked to identify erroneous sentences and correct them. In this paper it has been proved that the learners, in fact, have failed to learn a considerable part of what they have been taught. It has also been established that neither gender nor native language can be considered relevant factors in the students’ learning ability. As for the most difficult part in the Spanish language it has not been possible to identify a generalizable result, but a few errors that can be found in more than one of the investigated groups, and therefore point out vital problems in the acquisition-process, has been identified. In conclusion, this paper shows that the knowledge of the Swedish students need some improvement, especially when it comes to ensuring that the learners won’t keep making the same mistakes over and over again.