To have a basic number sense is important for mathematical understanding. Interventions in preschool class has shown significant positive effects on student’s mathematical development throughout elementary school. The purpose of this study was to find out the effects of individually designed intensive training on some preschool students with inadequate number sense. The intention was also to demonstrate how the intenvention could be designed as a preventive measure according to the reading, writing, counting guarantee introduced in Swedish school law on July 1st, 2019. The FoNS framework's eight categories, which together constitute basic number sense, has been used as theory and action research was chosen as a method to gain further knowledge of one's own practice and how to further develope it. A quantitative approach in form of a single case design with comparative figures has been used. The study also has a qualitative approach, by analysing the figures qualitatively, and putting them in context. The result showed that a structured, individual intervention can develop significant effects of the number sense. Six preschool students, at the age of six, who in surveys showed shortcomings in the basic number sense received intensive education for five weeks, three times a week, in pair. The study showed that short, intensive interventions can have a good effect if they are individually tailored, structured, well-planned and performed with few students at a time. Four of the survey group's six participants made a marked increase in results from pre- to post-test. Two pupils will need further efforts to achieve an age-appropriate number sense. The study shows that early intensive tuition in mathematics can be a preventive way of working for the special need teacher to prevent math difficulties.

En god taluppfattning är grundläggande för förståelse i matematik. Forskning (Lundberg & Sterner, 2009; Sayers, Andrews & Björklund Boistrup, 2016) visar på hur viktig barns tidiga matematiska kunnande är för goda skolframgångar i matematik i grundskolan samt att tidiga insatser i matematikundervisningen verkar främjande för elevers matematiska utveckling. Med utgångspunkt i detta har denna studie undersökt i vilken mån förskoleklasselever, med påvisad bristfällig taluppfattning, kan utveckla förståelse av antal och talraden. Detta med en tidsbegränsad och strukturerad undervisningsinsats med fokus på dessa två delar inom taluppfattningen. Som kartläggningsmaterial för att undersöka elevernas kunskap i taluppfattning användes Elevintervju vid skolstarten (McIntosh, 2008). Utformandet av undervisningen i interventionen tog sin utgångspunkt dels från resultatet av kartläggningen, dels från boken Tänka, resonera och räkna i förskoleklass (Sterner, Helenius & Wallby, 2014) och genomsyrades av ett sociokulturellt perspektiv på lärande där det är i det matematiska samtalet i gruppen som elevernas förmågor och kunskaper utvecklas. Under interventionen användes olika representationer för tal, exempelvis konkret och visuellt material för att stödja elevernas matematiska förståelse. Resultatet av studien visar på att en strukturerad undervisningsinsats gav positiv utveckling för den aktuella elevgruppen i denna studie, vilket är i linje med tidigare forskningsresultat (Sterner, 2015; Vennberg, 2015). / A strong number sense is foundational for mathematical understanding. Research (Lundberg & Sterner, 2009; Sayers, Andrews & Björklund Boistrup, 2016) has shown strong evidence of the relationship between student’s mathematical abilities when starting school entry and their later performance in mathematics. An early intervention in mathematics has significant positive effects on the student’s mathematical development through elementary school. As a continuation from this prior research the present study examined how preschool-students, with inadequate number sense, can develop an understanding of quantity and number sequence using the support of a structured and time specific intervention with focus on those two parts within number sense. Student interview at school entry (McIntosh, 2008) was the basis for examining the student’s number sense. The structure of the intervention lessons was based on the results from the survey and from the pedagogical literature Tänka, resonera och räkna i förskoleklass (Sterner, Helenius & Wallby, 2014). A sociocultural perspective pervaded where it is assumed the students’ abilities and knowledge develop from mathematical collective reasoning. During the intervention different representations where used, for example concrete and visual material to support the students mathematical understanding. The result demonstrated that a structured intervention in this study had significant effect on the group of preschool-students, which supports research (Sterner, 2015; Vennberg, 2015).