Evidence-based practice is highly appreciated and demanded in the field of education, especially in relation to extra support provided for children struggling with learning. Currently, there is a lack of intervention studies in the area of mathematics. This study aimed to investigate the effects of a short mathematics intervention programme on second graders (M[subscript age]?=?8?years, 2?months) with low performance in mathematics, in a quasi-experimental, intervention-control setting. A group of low-performing second graders (LOWi, n?=?11) was taught twice a week for eight weeks on the mathematics topics of number word sequence skills, counting skills and conceptual place value knowledge. The intervention's effectiveness was examined by comparing the mathematics performance of the LOWi group to those of two groups consisting of low performing (LOWc, n?=?13) and typically performing children (TYPc, n?=?64), who followed their business-as-usual mathematics instruction. The LOWi group made significant improvements in mathematics but did not show significantly better gains, compared to the LOWc and TYPc groups, immediately and three months after the intervention. We discuss the implications for educational practice and intervention research.